The sewing room is the sewing room! If you have to have a place for guest...buy a really nice air mattress with a pump and just create some floor space.
When I go to friends in Louisville, Kentucky I sleep in the craft room and stay awake half the night thinking about what I could be working on while everyone else is asleep! Too bad the serger makes soooo much noise. You oughta hear em in the morning wondering what that strange noise was they kept hearing :-D