I use two deer sleds as if they were drawers. you can use them under a platform. depending on where you end up, you can use one to haul things as well.
Second the bed rug. Very durable product.
I have been driving pickups with canopies on them for around 50 years. I sleep in the back of the truck often. Very handy in the wind, cold, and snow. A rubber mat on your truck bed and a mat on the tailgate help a lot. I like an 8 foot bed, then there is plenty of room to more some camping equipment over and have room for a bed roll and my dog. I like to use a small plastic tub for a table. A place to empty the pockets, keep a water bottle, etc.
I use a long handled broom to pull items out of the back of the truck without climbing in.
It is possible to build a platform to sleep on with storage under, but it takes a big drawer to be able to find stuff. Lots of people build cabinets, and storage, but it adds a lot of weight. In a full size truck with a long bed there is plenty of room.