When you check in there is a fairly large lounge area like they have at the airport. In my experience, most people are either in line checking in, checking out the model of the ship or getting their pictures made with a character. You can probably at least find a semi-quiet corner of that area with a nice couch to sit on. If you go early, the check-in process doesn't take that long and you can get on the ship and find a nice breezy deck chair on one of the less active decks.
I'll be doing the same with a 7 month old on the repo cruise. I'm hoping that I can at least get him to the occasional bottle stage by then so I'm not trying to nurse in an evening gown on formal night! DH and I haven't dressed up like that since we got married 10 years ago so I hate to give that up.