Just to say that if any of you have a real bad back, please don't buy an orthopaedic mattress - advice given to me many moons ago by my physiotherapist. They are fine if you don't have a back or spinal problem, but if you do to start with, these mattresses can cause you so much pain and prevent you from resting and sleeping. Vicious cycle then lack of rest, more pain.
I have a good firmish base mattress and I also have a tempur type mattress topper, and I think it is so good. I cannot see the need personally for a full tempur mattress, as you only sleep on the top, so why pay all that money ? Maybe buy two mattress toppers, they aren't all that expensive - well mine wasn't anyway.
Only my own thoughts on this.