Where are you staying? The Murphy Beds are practically toddler sized at Caribbean, Poly Villa, GF Villa, and Port Orleans; as is the fold down couch bed at the Poly.
When my guy was small and in that in-between time (too big for a crib, not yet ready for a full height big bed), we traveled with a kids Aerobed. They are designed with sides that are raised so they don't roll out. Small enough to fit into a little duffle bag that we either checked as luggage or stowed under the seat in front of us. I'm pretty certain they still make them....they do...and there are competitors as well: https://smile.amazon.com/s/ref=a9_s...&keywords=kids+aerobed&ie=UTF8&qid=1510335210
When my guy was small and in that in-between time (too big for a crib, not yet ready for a full height big bed), we traveled with a kids Aerobed. They are designed with sides that are raised so they don't roll out. Small enough to fit into a little duffle bag that we either checked as luggage or stowed under the seat in front of us. I'm pretty certain they still make them....they do...and there are competitors as well: https://smile.amazon.com/s/ref=a9_sc_1?rh=i:aps,k:kids+aerobed&keywords=kids+aerobed&ie=UTF8&qid=1510335210