Thought; on my son’s 2019, which has about 150k on it, the rears were worse than the fronts. We replaced the rears only, (bilstein 4600) and that alone made a huge difference. I’ll say the rears are much less labor-intensive - easier DIY, or cheaper labor. Might try that first and see if it’s all you need?
As for compressing springs - I don’t like to do it. I don’t work on vehicle suspensions enough or have the right kind of mentoring to feel safe myself, and I do have a lot of wrench time. As far as buying an assembly, it’d have to be a higher end brand (not Monroe or Gabriel, or rancho (which is Monroe). If eibach offered, I might consider. I would consider a set of fox coilovers, which I believe use eibach springs (?), but it may change the ride height. A lot of the preassembled stuff has thinner spring material or crummy bearings and bushings. If none of that sounds great, OE is likely tokico (sp?) and they are a quality shock. You might check tirerack since they have an easy storefront and decent quailtiy kits in general to see what they have.
That said, if you can change a tire, you can change a rear shock on the 4Runner. There is a top nut, and a bolt on the bottom. You’d need a basic ratchet set, a set of metric wrenches, and an adjustable wrench or something to keep the shaft from rotating as you loosen the top bolt. (Assuming it’s not too rusted).