Are you looking for the mattress only? Or for the mechanics of the bed?
If you are considering the mattress only, my advice is to check out Sam's Club and similar places for a good quality memory foam mattress topper. A couple of years ago my husband started having back issues with our mattress. I talked him into trying a king-sized mattress topper made out of memory foam, probably similar to this one:
http://www.samsclub.com/sams/4-press....ip?navAction= . We are still using it! Recently my brother wanted my help to buy a new mattress. I talked him into trying the memory foam topper first, and it worked for him also. If you don't like the memory foam topper, I would expect you wouldn't like a Tempurpedic mattress either. If you do like the topper, you may not need the mattress.
Edit: Check the store's return policy if you purchase the mattress topper. I know that I was able to return a memory foam pillow to Sam's Club. If you don't like the mattress topper, you may be able to return it.