For the mattresses, either some thick toppers or a new thicker mattress. Something like this : https://www.mattressinsider.com/memo...attresses.html
I do not boondock so I have no idea on the fridge.
Congrats on the new camper.
1 tip. Place some foam on the top corner of the livingroom slide. I am over 6 feet and had dented my head a couple mornings. I used the corner foam that is made for tables to protect children. Comes with double sided tape. My head is happier now.