4" Truck Sleep Reversible Mattress anyone use one?

Hi Everyone new to the the forum. Just got a Leer 100XR and plan to start sleeping in there while traveling. I found this http://www.walmart.com/ip/37245548?...40178495&wl4=&wl5=pla&wl6=79437754095&veh=sem.

Wondering if anyone has any experience with this.
Its 4" of high density foam walmart also offers one with 4.5" high density with 1.5" memory foam would that be better? The 4" come in 28"-73" which would be perfect the 6" 39"x75" so I would need to cut or just use that as a little more headrest. Im young and single so dont want to spend to much especially since im moving and starting a new job soon.

Opinions they are about the same price the 4" is a little more practical but the 6" im sure more comfortable and nice to have when the girls do want to crawl in? I guess im leaning toward the 6" now.

Here is the 6":
http://www.walmart.com/ip/12177337?...44869832&wl4=&wl5=pla&wl6=41449179889&veh=sem