I've mentioned this before, but it's an idea I'm completely sold on, so I think it's worth mentioning again.
If you're considering a foam type mattress, I highly recommend "building" one yourself. Advantages include:
1) Being able to pick materials (poly foam, memory foam, latex, etc).
2) Being able to pick individual layer and total thickness.
3) Being able to inexpensively swap mattress "components" until you find the perfect combination for you.
4) Being able to replace components as they wear out and/or one's body changes.
5) Nearly an order of magnitude cheaper than name brand equivalents.
6) Minor issue, but one can actually lift the 3"-4" layers by themselves. Moving a 10" thick foam mattress alone can be a pain.
I had no issues dropping $4K on a good mattress, if I knew it would remain comfortable for many years. But I just couldn't convince myself that laying down for a few minutes in a store was going to insure that.
Going the DIY route, I assembled a Tempur-Pedic equivalent king size mattress for less than $450. If anyone's interested, send me a pm.