I have back problems ( IDET procedure performed on L5-S1 about 90 percent improvement, and since December of 2019 upper back problems), and so does one of my brothers (2 surgeries on a bulged disk also L5-S1, last one last spring of 2020 and resulted in damage to spine nerves for one of his legs but before the operation he literally could not even stand up). I loved my 1985 Olds 88 2 door with the 60/40 front seat that I got out of a 1983 Olds full size station-wagon. And tolerated our 2001 Impala. When it comes to nice rides that absorb bumps in the road the weight of the vehicle means a lot. The big heavy vehicles that get poor gas millage absorb bumps in the road, and the small light weight vehicles that get great gas millage get tossed around and have a rough ride that aggravates bad backs.
Another thing is never put expensive high performance shocks on a vehicle that you want a nice ride from. They are too stiff and will transmit bumps in the road to the vehicle. You want to use the lowest cost shocks if you ever replace them. They will not last as long, but they will not make the ride bumpy.
Also other very important things to keep in mind when looking for a car with a good ride:
1) You do not want big rims with a small amount of tire between the rims and the road. You want small rims with tires that have a lot of rubber between the rims and the road to absorb bumps in the road.
2) You do not want a sport edition of any vehicle. The sport editions have big rims with tires with a small amount of rubber between the rims and the road, and to make the ride even bumpier on bad roads the sport edition of vehicles have a stiff suspension so they can go around bends fast and not have body roll, and do not have much body sway at high speeds. But the stiff suspension transmits bumps in the road to the vehicle and to the back of the persons in it. IT IS VERY IMPORTANT TO NEVER BUY A SPORT EDITION OF ANY VEHICLE FOR ANYONE WITH A BAD BACK. THIS CAN NOT BE EMPHASIZED ENOUGH. SPORT EDITION = VERY BAD BUMPY RIDE THAT IS VERY HARD ON THE BACK.
When I was shopping for a new to me vehicle late last year and early this year ride and long term reliability were top items on my list. I tried some small cars for gas millage but the bumpy ride quickly convinced me that I would have to look at bigger vehicles. The Honda CR-V in the EX or EX-L versions have big tires with 17 inch rims that provide plenty of rubber between the rims and the road. The touring models have 18 inch rims that have a little less space between the rims and the road. It turned out that the Honda CR-V went through several design changes in the past years. In 2015 Honda used CVT transmissions for the first time in the CR-V and it improved MPGs. However the 2015 CR-V has an engine vibration problem that Honda never took responsibility for but has an improved radiator mount that the customer can pay to have installed, and also has a rear end vibration problem that Honda never came up with a fix for, for the 2015 model year, but the 2016 CR-V had that those problems about 95 percent fixed. both still could happen but very rarely, and not anywhere as severe, and if you turn on the headlights or AC to increase the load on the engine so it does not go into the extra low RPM idle, the engine vibration never happens. In 2017 Honda went to a 1.5 L engine with a turbo charger for the CR-V (though they kept the 2.4 L normally asperated engine for the base LX model for a few years). The 1.5 L turbo engine has problems with fuel getting past the cylinder and into the oil.
So the sweet spot for the years for the used Honda CR-V is the 2016 year. And I test drove a 2016 CR-V EX and the seats were comfortable for my back and the vehicle absorbs bumps in the roads well, so I bought it. One thing is the large tires on it also roll over small holes in the road without even entering into the hole which means that small holes in the road cause no bump at all. I did experience the engine idle vibration problem once, actually when I test drove it with the headlights and AC off. And I experienced the rear-end vibration problem once, a couple of days after I bought it, but the rear-end was slightly out of alignment and the dealer aligned it properly with a Hunter alignment machine that measures angles down to 1/100 of a degree, and since it was properly aligned the rear end has never vibrated again. When I drive it I always turn on the head-lights anyway, so I never have the extra low RPM idle vibration problem because the engine never goes into the extra low idle RPM range with the head-lights on.
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My brother with back problems loves the seats and the ride of his 2007 Nissan Altima Hybrid. And he says the seats and ride of his wifes more recent Nisan Murano is even better.
I have heard it said that Nissan copied the zero-gravity seats designed by NASA for its vehicles, and that these seats are very comfortable and good for people with bad backs. However there are many people who say that the CVT transmissions that Nissan builds themselves and uses in there vehicles is not a good design for long term life and can not be fixed when it goes bad, may cost $6,000 or more to replace with a new one. I understand that in the Murano the front of the vehicle must be removed in order to replace the CVT which increases the labor cost to have the total cost much higher than $6,000 to something like $10,000 or more.
Note that the 2007 Nissan Altima does not have a Nissan drive-train and does not have a Nissan CVT. The drive-train for the 2007 Nissan Altima, including the transmission, was made by Toyota that year. Now the Nissan hybrid drive-train is made by Nissan. I do not know what year that started.
The Nissan CVT transmissions had so many problems that for some years Nissan stopped using them in the Murano.
When I was lookin for a vehicle I stopped by a very big transmission repair shop ( they have 10 lifts ) and asked the owner if Nissan still has problems with there CVTs and he said "yes, they still break often when they get high miles on them."
So if you are going to get a Nissan, either plan to dump it around when it gets around 70 K miles on it, or change the CVT fluid on it very often.
So the vehicles that I know to have a good seat and a good ability to absorb bumps in the road are the 2016 Honda CR-V EX or 2016 CR-V EX-L and any year of the Nissan Altima or Nissan Murano.
The Honda CVT does require frequent fluid changes ( somewhere between every 25 K miles or every 35 K miles ) and in the AWD versions the rear-end differential also requires fluid change every 15 K miles ( though it only takes 1.5 quarts). However oil changes, CVT fluid changes, and rear-end fluid changes, are all very easy to do on them, and also there are YouTube videos of how to do them. For reliable performance you should use only Honda fluids for the CVT and rear-end ( note, if you do both at the same time, be darn sure you do not mix which one gets which ). You can get lowest cost Honda fluids and parts from Bernardi Parts.
So the bottom line is, I with my bad back, like my 2016 Honda CR-V. It has a nice ride that absorbs bumps in the road well, and the seats are very comfortable. The lower half of the back of both front seats and the bottom of them has a heater that has 2 heat settings and that is also nice for anyone with low back pain. When C-19 is no longer a problem, I may get a local good upholstery shop to add heating to the upper part of the drivers seat, because I have bad back pain in both my lower and upper back.
My brother with a very bad lower back pain likes the seats and ride of his 2007 Nissan Altima very much, and his wifes more recent Nissan Murano even more.
One other thing I will mention is that I am 6' 4" tall and my brother is 6' 7" tall so since fit is also a very big part of seat comfort, if the person with the bad back is shorter than that, they should try the seats to see if they are comfortable for them.