I've decided to start looking for a mattress, because I've been sleeping on a mattress that I inherited from my grandparents. I think it's a good mattress - it's a Serta Perfect Sleeper "Ciera". But it's at least 34 years old, because I remember them having this bed and mattress set from the time they moved into their house in 1983. I inherited the bedroom furniture set, along with the bed, in 2001, when my grandmother died, and I've been sleeping on it ever since.
It's in good shape - I flip it often, but in the last year or so I've been noticing a little lower back stiffness/soreness. Nothing bad, but it makes me think that maybe the mattress is not supporting that area very well. There's no bad sag in the center of the mattress or anything, but it does seem just a little bit saggy in that area.
Anyway, I've decided to start looking around. And, having never bought a mattress before, just like the OP said in the title, my head is spinning!
Just a little info about me - I'm 6'2", 180 lbs, and I am planning on staying with this frame and box spring set (as long as there's no reason to swap out the box springs). I do think I will want something firm. I've done a little bit of reading, and I'm sort of suspicious of the memory foam, because, for one thing, they say it gets hot, and I'm already hot-natured and sleep with 2 fans blowing on me.
Also, I tend to sleep sort of equally on all sides - back, stomach and side. Typically I'll go to sleep on my back or side, then roll over onto my stomach at some point about halfway through the night.
I don't think I'm interested in an air mattress, because I don't think I'd ever care about adjusting it to be firmer or softer.
I think my main concern would be that it maintains support for years.
Money-wise, I'm not sure, because I just started looking and haven't gotten an idea yet of what's available and for what prices. I tend to be someone who wants quality, but doesn't have to have the absolute best. Like anybody else, I like to get a lot for my money.
With most of my purchases, I feel that, at some point, returns are diminishing, and I typically buy around that point - say, a 7 out of 10. So, I don't mind spending some money, as I believe the initial pain of spending a little more will be forgotten long before the regret I might have from cheaping out.
Anyway, I appreciate the info everyone has already put into this thread, and obviously I welcome any additional info/opinion anyone wants to add.