I brought my daughter when she was tiny to Disney World several times & what really helped me were Disney's Baby Care Centers & taking a break midday for naps at the Resort. Glorious naps, how I miss thee!
The Baby Care Centers are conveniently located in each Park, the locations will be clearly marked on your Park Map with a picture of a pacifier. They provide a quiet, comfortable place to change diapers, feed the baby or even just duck in when the baby has had enough and needs a spot to chill!
Another good thing to know about is using the "rider swap", also known as "baby swap" when there is a ride you both want to do, but can't bring baby on. You & your partner stand in line together & then one of you gets to ride while the other one holds the baby & then you swap!
Here is a link to Disney World's Traveling with Little Ones advice & tips:
Bring a stroller that is easy to maneuver & folds up easily if you are using Disney transportation. One time I had a stroller that wouldn't cooperate when I needed to hurry & get on the bus & I could have cried it was so frustrating! I also brought a sling as backup.
I hope you have a wonderful trip that will bring a smile to your faces for years to come!