We didn't want a corner bed either and bought a small class C (25.5 feet) with a rear slide out the back end of the RV for a queen bed. Before the slide comes in, the top third of the mattress has to be folded in. I thought it would be a hassle but it's really not - a minor adjustment of the bedding when it goes in or back out again.
The mattress is memory foam and we both find it comfortable and sleep well on it.
There's a very skinny "aisle" on each side of the bed, and though I don't really consider it a "walk-around", it definitely makes making the bed easier and getting in & out on the sides. It takes standard queen sheets sold anywhere, another plus.
Ours is a Navion, but there are several brands offering a similar queen bed slide out the back.