I have a memory foam mattress pad (3 inch) on top of a firm foam slab that I bought from Penneys. Best mattress I've ever had. I gave up on the expensive mattresses. We've had this set up 10 years and counting. Will not give it up.:)
Edit: I have arthritis and have no problems with stiffness in the morning. Similar to the Tempurpedic mattress as the memory foam is the basically the same stuff.