I agree that memory foam seems too non-supportive for me and I've tried 2, 3, 4 and 5 lb varieties.
What I am doing right now - and have done before - is to add a 1" piece of memory foam (in my case, 5lb) - about 6" wide - across my lumbar region under the top layer or even under a couple layers. This adds a little support. This is what Simmons and Sealy have done on some newer mattresses, more or less.
I would definitely go with the higher poundage of MF if you're going to try it as a complete layer.
I always find that it feels good for a few nights, a week or a few weeks, and then my lower back starts to hurt. But millions of Tempurpedic customers can't be all wrong! (Or can they? ;-D ) I tried Tempur too and had to return it!
MF is said not to be good for lower-back pain; let's your butt sag down too much. I did zoning, with 20ILD FBM latex under the hip area (it's really firmer than 20, most say) and 4lb MF under shoulders and all. I like it, but butt area still feels too firm, so have a piece of super-soft I'm gonna try on top.
