The allearsnet website has a whole section devoted to "Disney At Large" which details what type of seats each ride has and the challenges for Pooh size guests. Coming from a whole family of Pooh size guests, we've had very few uncomfortable sitations with Disney rides and never had a ride that we COULDN'T get in (Universal? That's a whole different story!). Considering your leg issues, at MK you might want to reconsider the Tea Cups, as the doors are narrow and there's not a lot of legroom. You might want to reconsider Space Mountain as well. If you have trouble steping down into rides (I don't know how the bandaging you are using would affect this) you might need assistance with getting into some of the boat attractions like Small World, Pirates, Jungle Cruise, etc, although the ride will certainly be roomy enough once you're in it. Disney is very patient about giving you time to get in the ride and get settled if they see you have a problem. One hint we've picked up over the years: If you are getting on any ride with a seat belt, pull the belt all the way out and hold it out while you sit down. Keep holding it out all the way until you get it fastened and then let it settle back. No one in our family has had trouble with seat belts since we tried this trick (nothing worse than a ride taking off before you're strapped in - it happened to Dad on Space Mountain back when it had seat belts, and he rode the whole ride with no restraints at all).
Basically, it all depends on where you carry your weight. If you carry it in the upper back/chest area, then rides with overhead restraints may not be comfortable. If you carry it in your stomach, lap bars may present a problem. If you carry it in your hips/rear, it can be theater seating that may be uncomfortable. Also, as you're going up to board a ride, if you notice the seat is a little narrow, don't be afraid to say you are two parties of one, instead of one party of two. It's OK to have your own seat instead of being squashed up together, and a lot more comfortable. Like I said, we've never had a problem getting on a ride, but some of them were less comfortable than others. I've never seen anyone at Disney try to get on a ride and not fit, although I'm sure it has happened as I've seen some extremely large people there.
Also, have you considered renting a
scooter in the parks to assist with your mobility issues? In fact, you may want to check out the disabilities board for off property rental companies, so you can have it with you the whole time. Most people end up walking 5-10 miles PER DAY while at Disney, and it doesn't sound like you're up to that. You'll see a lot of people using the scooters, and it can really make a difference in the quality of your trip. I had a hard time talking my Mom into using one, until we went on a trip to MK, and had to leave after two hours because she couldn't make it any farther. Ever since, we've rented one and at the end of the day, she still has enough energy to enjoy the resort and have dinner in the restaurant instead of having to order room service. One good thing about the scooters is that you can stay on it for most of the theater attractions/shows, so if the regular seats were going to be uncomfortable due to size issues, you won't have to worry about it.
I have found that no matter what my size, there has always been someone larger, and no matter what my (or my family's) mobility issues are, there is always someone who has it worse than we do. The important thing is to relax and just have fun.