I would also speak to the doc/therapist about taking along a gel pack to freeze and have available to ease any swelling. Also, check into other things like elevating the knee when lying down. At least during Dec., you won't have the intense heat of Fl, which will help also. Your doc may want you on an anticoagulant if you aren't already.
If you take a wheelchair and are flying, you can ride straight to the door of the plane and the flight attendents will take the chair to the cargo area and it's waiting for you at the door of the plane when you disembark. Call the airline ahead of time.
Also, if you rent a car, make sure it's large enough to accomodate the chair and any limitation of knee function, by that I mean that the door opens widely and you have enough leg room.
You probably should ask for first floor accommodations and I think there may be shower chairs available through housekeeping.
The cast members at the attractions are wonderful about accommodating the physically challenged. Just let them know when you approach.
Have a good time.