There have been previous discussions about beds that you should be able to
access through Google groups.  I don't use any of the special ones right now,
but here's what I've gleaned from past discussions:

Tempur-pedic mattresses are wonderful for some fulks initially, but they
don't seem to have a very long life at the wonderful stage.  Something about
the foam breaking down.

Depending on the state of your current bed, you might try adding a memory
foam topper for a while and see if that helps.

Lots of people like the quality air-beds, Select-Comfort is the widely known
brand but Comfort-aire is equally good and less expensive.  They usually come
with a 90 day free return and both have 25 year warranties.  There are slight
differences between the two so you might investigate both if you decide to go
that route.  (Mike doesn't know it, but I'm hoping to go the Comfort-aire
route when teh current futon gets too compressed.)