I too am Pooh sized and Disney is very accommodating. You shouldn't have any problems at all. I will give you a tip about the seatbelts on a couple of rides (Test Track and Dinosaur come to mind) - pull the belt all the way out while still standing, see the connector and go ahead and secure the belt as you sit down. It's harder to find the slot once you are sitting down and feel rushed, etc. Have fun!
Lisa
Tiger Fan