Hi Kristen!
You will have so much fun with your 9 month old! The first time my daughter went to Disney World she was 9 months old. :)
Of course, you'll want to bring a stroller and maybe a sling or baby carrier with you. My daughter fell asleep pretty good all throughout the day--which does make things easier sometimes!
She will love all the shows because of the colors and music. At Magic Kingdom, most of the attractions will be appropriate for her (not the roller coasters, of course!). In Epcot's World Showcase, she'll love looking around with you. And in Future World, there is lots to see and feel and touch.
Have you seen the
Traveling With Little Ones part of the Disney site? There's some really good tips and a fun printable map that highlights all the attractions that are most appropriate and attractive to little bitties. :)
My favorite memories from that trip with my daughter was getting her first haircut at the Magic Kingdom's Main Street Barber Shop and seeing her get pictures with the Princesses for the first time. It was truly magical!