what about trying something like these?
"wedges for bed comfort"
http://images.google.com/images?hl=e...-8&sa=N&tab=wi
We have an 80% waveless waterbed mattress with built in lumbar support -
and we did add a tempurpedic type topper when hubby pulled a back muscle and we both liked it so kept it on.
The tempurpedic stuff does hold in body heat so depending on location and health situation it could be good or not so good.