I am sorry to hear about your back pain! If you are planning to go to a 1-800-Mattress, they will be able to answer alot of your questions there. I have actually been quite pleased with my past experiences with 1-800-Mattress. I also had some back trouble (bad sciatica) and they knew about my condition and made alot of suggestions for me. I was very impressed. Be careful with Tempurpedic, but try it out. It is either great or too hot. (I find them very warm.)
I am sure you will have the same experience!
Hope you feel better!