I'm also allergic and a non-smoker.
I find it best to book on a deck with some other things on it. In particular, on Shadow, the first day we felt a lot of smoke in the hallway (stayed in 611). The long hallway was the issue. Nothing has ever affected us in the cabin itself. On that cruise, they did haul out heavy duty machines, and this was gone in two days, but it did happen.
