I need my daughter's room to double as a guest room when I have people in town. I live in NYC, so space is limited, and I want to get a pop-up trundle bed so it can convert to a King when we need it. The top part of a trundle can accommodate a regular height mattress (10") but basically every trundle option on the market only accommodates a 5" mattress beneath.

Since my parents are getting older, and would likely use this bed when they visit, I was thinking of getting a 10" mattress, and 2 5" mattresses so they can have a 10" mattress when they come stay, since I've read that 5" will not be great for them as they age. In the day-to-day, I'd stack the 10" + 5" mattresses on top, and leave one 5" on the bottom. My daughter would sleep on the combined 15" mattress, and when it's time to expand the bed I'd stack the 5" mattresses together so the bed is flush.

Am I just asking to ruin all of my mattresses, or could this work? I'd buy mattress protectors to avoid any mildew forming, but not sure if I'd ruin the comfort of the mattresses this way.