YEAH!!!! That low back thing is pretty much what I found too. If my rear sinks as far as it will with gravity and doesn't have a force pushing back, low back tries to pull back out of the hole. Or it might just fall far enough that it pulls my spine out of alignment.
For future reference, if some tweaking of above is sometime necessary....I've found a couple of simple solutions lately. They sound weird, but seem to work...
I had two polyfill mattress toppers on our bed going across instead of up and down(one was twin size, at feet, covered the lower third of the mattress, the other was a full size and covered the rest). The one under our hips and shoulders felt too soft at some point, and I took it off. The lower one was fairly flat and for some reason I left it(under the mattress pad). Oddly, it seems to help with low back pain. I sleep better with my legs very slgihtly raised rather than flat. No idea why. I re-discovered it was there and took it off, and had to put it back on after a couple of nights.
The other thing is that I sleep with a small polarfleece blanket folded to about 10" wide by I don't know how thick..not very...under my upper thighs. That helps my low back. When I'm on my side I stick it between my thighs, like that side sleepers pillow, in that hollow between your knees and your upper legs. I also found that if I can make my top leg go lower than my lower leg it pulls the curve out of my spine and no backache...my knees are not even, the top one pulled over the lower one.
Anyway, sounds like you are on the right track...nice to achieve success eventually. I'm not far behind you on the $ scale. Sick of throwing good money after bad.
Kait
