I'm also doing NYC to Bermuda in January and I'm also thinking about sweaters.
The internet claims average temp in Bermuda in January is 70 for a high and 60 for a low, and can be rainy. That to me is chilly, I am one of those always cold folks, so I'm bringing more lighter layers and fewer summer clothes. I'm basically planning on dressing for casual early fall/spring with some flexibility.
I'm planning on wearing a Columbia zip up fleece under my lightweight Columbia omni-heat jacket for boarding, instead of a big winter coat. So that should cover me for anything from snow in NYC to a rainy day on land to chilly night on deck. Either piece can be stuffed into a carry on.The Columbia stuff isn't officially rainwear but I've noticed it's decent at shrugging off light rain while staying warm.
I'll probably bring three of those light, drapey Jersey knit cardigans to throw over nice tops or tanks and black skinny jeans for casual evening outfits. Daytime is casual, I tend to live in Columbia hiking pants. I swear, I don't work for Columbia. I just like how practical the clothes are and they travel so well.
I haven't figured out formal night, I'm on NCL and not inclined to get super dressed up, maybe a cute velvet dress and flats. I'll bring a sun dress in case, which I can wear with one if the cardigans if it's chilly.
So basically I'm bringing my usual fall clothes with a couple of summer outfits in case we do get a warmer than normal day. The nice thing about the layers is that they're all light so they pack easily and if you need to hand wash, they dry quickly.