I don't do movies in the theater, but I what I would normally do in this situation is start out overly cautious and then step back slowly. So if this time you took sheets, maybe next time, go sheetless, but look at the seats and still change clothes. If that's fine, maybe next time you don't all need to strip when you get home.
Though you didn't say if you ate at the theater...I think that if I was eating while I was there, I would want the arm-rests covered or at least wiped down so I didn't touch them and then put my fingers near/in my mouth, since I've had contact/ingestion ana. But otherwise, I'd go with a gradually stepping back method.