We bought a Class A motor home that had a King Size sleep by number bed. We have had that kind of bed before and didn't like it then. While at Shangra La Ranch in Arizona we decided to get rid of the bed. We traded the bed for our camping bill and bought a Queen Size mattress from a regular store.
After a lot of measurements we found a carpenter, I didn't have enough tools with me to do the job myself, to cut down the bed base to fit a Queen Size mattress. We droped the mattress on the bed frame and have slept soundly ever since. We also don't slam our fingers on the bed side tables when we make up the bed. There is room to stand in front of the closet and look for what you want.
My suggestion is to replace the mattress and sleep comfortably.
Chuck