Simmons ComforPedic memory foam mattress?

[Surfrider]

I bought a decent quality, firm mattress at Sam's, put it on a platform. Bought 4" memory foam (the firm stuff, not the Walmart stuff, got mine on Ebay), put it on top, and I sleep well, back pain and all.

The whole deal cost less than $400 and I've had it for 8 years.