The mattress came from a very comfortable queen-sized bed with a memory foam mattress.
Being of the "Mend and Make Do" generation, my wife took a bread knife to it and then covered the two resultant single mattresses with surplus sheet material. Machine and then hand stitched to close the end. We have elasticated bed sheets to pop on in the van.
I have just measured the mattress. It is actually a bit over 8 inches thick, 30 inches wide and 6' 3" long. Very, very comfy, I have slept on it indoors this winter when ejected from the marital pit by snoring!
Photo of the modified van attached, just coming out of winter hibernation, the mattresses are still indoors. You will notice I have also removed the obsolete electronics and my first job this year will to finish off removing the old shelving and wiring and to fit new bed reading lights.
Before the major expense and HASSLE of replacing your 'fridge, I would check the 120V circuitry for blown fuses or other faults. If the fridge works on LP gas and 12V, the refrigerating part is fine, just the 120V heater not working. The 120V heater itself is easy to replace and not expensive - plenty of "how to" information on this forum and YouTube.
2008 Pleasure-Way Excel-TS
1998 Auto-Sleeper Pescara
1992 Autohome Frontier
1973 Bedford CA clam-shell rising roof