I agree with the other's. If your son is that sensitive to smoke, another cruise line (or maybe another vacation choice) is worth looking into. Otherwise, you'll need to use the elevator's to avoid the smoking areas as much as you can. (On our cruise on the Conquest you had to walk outside the wide open Casino to get to restaurants, bars, shops, etc., unless you went up or down a floor.)
Besides the possibility of smoke, there will also be other "triggers" to consider. For instance, some people wear enough cologne or perfume for everyone
on the ship and it lingers.
There will also be the odor of cleaning supplies and bleach (which bother's me).
I hope you'll all enjoy whatever vacation you choose