We just got back from a three-night cruise on the Dream (our first cruise ever!) with my tween and 22-month old. We traveled with both kids as infants and toddlers and I think the best advice I can give you is whatever you decide to do, adjust your expectations. It's too early to know what your little one's personality will be like. Will DB love the nursery or will you get a message 15 minute into dinner saying "we are trying to calm her, but she is extremely upset?" Will he sleep through the night? or stay up all night and want to sleep all day. Having a kid amaaaazing, but it's the hardest thing I've ever done.
Here's how our cruse went. DD did great during boarding and muster (yay!) after that she started demanding to go "night-night." We held her off long enough to take a quick look at the nursery, then I took her to nap while DH and DS checked out the kids club and tween club. She was still napping at dinner time (5:45) so they went on without me and our server was kind enough to package dinner for me, which my husband and son brought up. DD was so tired she slept through a loooong in-room announcement. We had a 6:30 nursery reservation so woke her a little after 6:00 and got her freshened up. She was happy and stayed in the nursery until we picked her up around 9:30. They commented on how good and happy she was. The next day she didn't nap as well. We all ate dinner together and she was grumpy and a handful. It was miserable. I tried to take her to the nursery but got a message around 30 minutes later that she was upset and cried unless someone held her. The staff was willing to keep trying, but I know my girl and it wasn't happening that night. The next day was our anniversary. DS would not nap at all. At dinner, we sent the oldest off to the tween club and tried again with the nursery for DS. This time my husband dropped her off and let the staff know it was our anniversary. We had initially wanted to have dinner and see a show together, but by that point, we would be happy making it through dinner alone together. We did make it through dinner. I checked in on her and she had fallen asleep watching Mickey and the Road Racers. DH and I enjoyed some alone time and shopping before she woke up and we got a message that she was upset but they were trying their best to calm her. DH went and picked her up, and we watched a movie in the room before packing.
Traveling with kids is not relaxing. It is hard. There is more stuff to carry and a lot less time to have fun. One or both of you will be in the room for long stretches of time. We did not see a single show or movie during our cruise. We still had fun and enjoyed being together, but we knew going in it was going to be tough sometimes. If my son hadn't been about to age out of the kids club (he wanted to do the Star Wars stuff) we would have put this off longer. We tag-teamed as much as possible so we could do some activities with DS, but a lot of our time was devoted to caring for our toddler. And she's a pretty good traveler and generally a happy kid.
Another thing to keep in mind is, it is easier to travel pregnant than with a baby. We did a family trip to New York when I was near the end of my second trimester and I got tired from time to time, but we still got to do way more stuff than we would have with a baby. If you can move up your trip you might enjoy it more, or you might want to think about putting it off until baby's closer to three.
Our first family vacation after she was born was very low-key. We rented a condo at a resort in the mountains. We drove. We didn't go far or spend a lot of money and it was relatively relaxing.
If it were me, I would take a small babymoon trip before the baby comes. Save some of the money you'd spend on a big trip for babysitters and date-nights after baby comes and for a family trip for around baby's third birthday. That's when I remember traveling getting easier with my son. When they are down to one shorter nap per day you can get out and do more.
If you decide to do the cruise, plan on tag-teaming the baby and be ready for things to not go as planned. You can still have fun, but you're going to work for it! Parenthood is great and you're going to learn and grow like never before. Congratulations and enjoy the ride!