My father in law has a pretty slick set up for his old chev pickup with an 8 foot bed. He just has a canopy shell on the back. I dont know the make of it, but has kind of a sleek shape to it (as opposed to a fully square shape), and the top is somewhat higher than the cab. The back has a door that is mostly plexiglass, although the whole back end can swing up for full access to the inside.
He's built what are essentially cabinets on the inside. They are just about even with the top of the truck bed, and wrap all the way around (side, front, side). I dont know how wide they are, but someone can sleep on either side. Because of the cabinet design, he has plenty of storage underneath the actual sleeping area. I dont know what he uses for mattresses. When when he goes camping, I know he is quite cozy and comfortable.
Now me, I need the TT with the stove, refer, bathroom, real mattress, etc