Sorry, but the best suggestion is to leave the baby home. If that is not a possibility, postpone cruising until he is old enough for the kid programs.
Babies on cruises is a very sore subject for me. Our very first, (and almost our last) cruise was absolutely ruined by the infant in the next cabin. It cried almost non-stop the entire 4 days. When IT stopped, it's toddler sibling took over. We are talking 23 out of 24 hours here. No sleep at night, no quiet time for a nap to make up for not sleeping all night. Obviously at least one parent, as well as everyone in earshot, were most certainly NOT having a good time. The cruise was totally booked, so there was nowhere else to move- believe me, I tried.
Please, please, please- leave the baby home!!!! If you want a family vacation, go to DisneyWorld- or at least take a Disney cruise- THEY have babysitters and everyone has kids. Leave the grown ups to cruise in peace. I cruise to get AWAY from the kids!