I haven't actually put down a twin sized air mattress, but my DD usually sets up a pallet on the floor in the studios. She doesn't want to share with anyone.
The two best locations we've found for her are: In the vanity area, either in front of the sink, or along the closet door. Or in the entrance area.
Both have their difficulties. The vanity area can cause problems when people want to use the restroom during the night.
And the entrance area gets quite a bit of hallway noise, particularly if you are near an elevator. I usually end up stuffing a towel under the door opening to muffle the sound and block the light.
My DD is VERY light sensitive, so being between the sofa and the verandah door just won't work for her.