Baby centers! Great cool break from the over-stimuli (parent too
I recommend a stroller - while I look forward to my first trip coming up with no stroller (yay!) I need so much gear and supplies for a little one, the stroller was just as much for "stuff" as it was for baby - and a way to get your arms and back a break when baby naps or you eat. If you use a stroller, consider a towel to dry it off after a rain or keep it shaded when baby isn't sitting (no burned buns when baby gets back in a hot stroller seat)
Be patient and flexible - if you go in planning a relaxed, "take it as it comes" trip you'll be much happier dealing with the diaper changes, rest breaks, etc. that characterize a day with baby.
White noise machine and clothespin to help keep curtains closed on your hotel windows. Bring a night light.
If flying, I like shipping myself a box of diapers, food, other consumables so I didn't have to lug it on the plane and it got used up on the trip, so nothing to bring home. If you do load up on souvenirs, you can always ship them back home in your empty box
Consider ear plugs - there is music and sound everywhere at Disney and some attractions/shows are downright loud.
If you don't take nap breaks at your hotel, consider sit-down lunches, long slow shows or rides (monorail, carousel of progress, people mover) for afternoon quiet times.
Read up on Child Swap /Rider Swap so the adults can ride a thrill ride or two while taking turns sitting with baby.
Have fun!!