In a nutshell, no there is no such thing as a walk-around bed in a truck camper. For such a thing to work the camper would be 15' tall sitting on the truck. Way over the legal limit.
The best you can hope for is a "crawl-around" bed.
Larger campers are quite roomy up in the cabover, and most campers these days have the popular North/South bed so you can get in and out without crawling over anyone.
BTW, N/S beds are not limited to extended/crew cab pickups. You can put one on a regular cab pickup, it just might look a little goofy and make seeing the traffic signals a little difficult if you pull right up to them.