That's pretty nifty since it fills the bed and fits around and over the wheel wells. I haven't used one but I expect there isn't enough padding to comfortably sleep over the wheel wells. Still, it might work well for you and it's not too pricey.

Under toppers, I have used a couple different bed camping set ups and have spent a few hundred nights sleeping in my truck beds while traveling or doing field work. Personally, I've never gotten great back support from air mattresses. I prefer high density foam. My current rig has a high back topper with a full Bedrug. The Bedrug is carpeted and has high density foam in and over the bed channels so you can move around on your knees. I can throw in the foam mattress to make a very comfortable bed and still have room for a camper supply box that doubles as a table that I can cook on.

I swear by the Bedrug as one of the best accessories on my truck. No matter what I'm transporting from boxes, furniture, whatever, things don't slide around on the Bedrug carpet. http://www.bedrug.com/products/bed-liners.html