As seen here1), a pickup with a camper shell (“topper”) can make a very serviceable dwelling.
Shells with a raised “hump” area will provide more headroom.
Camper shells can be very expensive when new, but tend to be much cheaper used. Gas struts and keys are usually easy to replace; glass can be tougher.
To get a good deal, make note of what camper tops fit similar vehicles to yours, and widen your searches to include those vehicles. Example: if you have a 1999 Ram with a 6' bed but notice that campers that fit yours also tend to fit a 2000-2008 Chevy 1500 with a 6ft bed, then also search for camper ads that mention the Chevy.2).
Pickups have recesses in the truck bed sides to allow boards to be placed across the bed; this is to allow the truck owner to carry large flat items like sheet rock and plywood flat over the wheelwells. You can place your own plywood across these boards to make a raised platform with storage underneath. Tupperware containers designed to store under beds are particularly useful here.
One advantage of sleeping on a platform rather than a built bed is you can sleep on the diagnoal in shorter beds.
One of the downsides of having a topper is you cannot reach over the bed to get stuff out. A grabber pole makes topper life much easier.
Attach a hook or L-brace3)) to the end of a length of a PVC pipe or dowel. With practice you will be able to push and pull items all the way at the front of the bed.
The pole can rest on the inside ledge of the camper shell4) when not in use.
For lighter items, rack rails can be bolted through the topper. Example: Thule
For heavier loads external racks that go around the topper might be useful. This type of rack can extend over the cab area for even more storage/mounting options. Example: Campway 3000