I use a fork [1] of Valetudo and it lets me do just this. I save one map per floor, then restore when carrying it between floors. One floor gets cleaned much more often, but so far I have preferred this over buying two robots.
Currently I can just get the robot from one floor to the next and press start. It takes a few seconds to find its bearings and switch maps, then goes on his merry way.
Having to restore a snapshot each time I move floors is a lot more friction.
