If you'll search the forum, you'll find dozens - if not hundreds - of threads on this topic. The advice to put the residential mattress of your choice in the camper is sound advice. With a residential mattress, 12" of thickness won't do anything except cause you possible clearance issues. Be aware, too, that foam mattresses require ventilation underneath to prevent mold - they can't just sit straight on a plywood platform. There are special substrates made for this purpose. We have a Tuft & Needle queen in the RV (we're full-timers) and it's the best mattress either of us has ever slept on... and we're old.
Rob
