Mattress fit/removal

My wife needs a legit mattress. I'm probably going to buy the memory foam we found that works in our bed. 60x80 firm (the opposite side is soft, like half and half?) and 10.5". Few things, since I'm designing, I know standard is 48" high with a 6-8" mattress, should I go 50" high or 2.5" not a big deal? Also many builds I've seen have 58ishx78ish mattress location (5' wide, minus walls, w/e length minus galley/front storage). Do y'all find custom size mattresses? If you put an actual mattress in, queen, you ever able to get it out? Since I'm building my own trailer, I can go 62" instead of 60, for a full 60" inside, I think anyways, at least the axle is custom and the tubing is custom, don't think it'll affect towing too much. I know with the 78" length any plans I can just reduce front or galley or add 2". Appreciate any thoughts.