Do what the others have said and if it gets too bad while you're down there, just rent a scooter. Even one days rental may help to relieve some of the paid. My husband had to rent one while we were there on our last visit because of an injury. He felt so bad having to do it, but couldn't walk very far either. So, he just rode it around most places and then just stood in the regular lines most of the time. I think the only time he ever took the scooter into an attraction was to see Philharmagic. The cm told us that if we hurried we could run and catch the doors before they closed. Well, no way could he run, so he just took the scooter in and just barely made the show. No one looked at him funny and no one judged him from what we could see for being on a scooter. They cost a lot, but at least you'd be able to enjoy the parks or at least know that that's an option to help keep you pain free to enjoy the parks! Good luck and have fun!
(P.S......the bed you suggested for my ds arrived yesterday and he LOVES it! Well, to play on it anyway and pretend he's going to bed. He'll tell us bye (which he says when he's going to bed) and then put his Mickey to bed with him and close his eyes. Now if we could really get him to sleep on it before our trip, that would be great!)