I needed to fly when our premature daughter (still on heart monitor and only 5 pounds) was only 3 months old (adjusted age about 1 month, she was 2 month early) It was a 2-3 hour flight. She was awesome. I couldn't really not go as it was my older son who needed to get to college (1400miles away~we drove him out so he would have car and flew home). All the restaurants, setting up dorm room, hotel, etc. just seemed to sooth her! Previous our youngest had been about 4-6 months to travel any length with our babies. Now I know better, they really only need one thing until about 6 months and that is their Mama (well, okay and diapers!). Oh yes, and she was delivered emergency c-section (not so fun) but at 2-10 weeks I was traveling daily back and forth to NICU each day so a 3 hour flight was a piece of cake. oh yes, and when she was 6 months old? (adj age 4 mon. and weighing 10 pounds by then) We took her to Disney!
I see you chose to delay a bit. You will have an awesome time! and Enjoy your new little one and Disney of course!