The apartment is lovely, the location is superb, and the hosts are
very friendly.

There are a few inconvenient aspects, though:

(1) The bed to sleep on is at the top of a very steep ladder (and is squeezed in a very narrow space under the ceiling). Not ideal for climbing in and out if you need to in the middle of the night, or if you're a bit inebriated (who isn't in Paris?).

(2) The toilet bowl is placed in a such a way that you can't really relax when you sit on it: your knees are tucked into the walls.

(3) The sink to wash your hands is underneath some sort of panel, so that you can't see your hands when you're washing them, and the faucet is tucked into the sink so that there isn't really room for your hands.

So, I'd suggest to the hosts to invest into remodeling of the bathroom area to make it more convenient. As to the bed, I'd suggest making an additional sleeping space at the floor level.