I found the same problem that Doc is mentioning with bouncing while driving. My wife and I usually trade off and my old spring mattress just wasn't cutting it when I was trying to get some shut eye. Someone recommended MattressInsider.com which has a few
foam truck mattresses to choose from. The down side is you can't try them before you buy. I couldn't find anyone locally who carried them so I just ended up ordering their
truck mattress with memory foam and I've been pretty satisfied.