asta,
My Sister and I are long time disney fans & travel there a few times each year. She is 40's and had her knee replacement sept 2011.
She waited far to long to have the surgery. I watched her hobble around wdw for years, then with her "loader brace". On a trip in 2010 October > a younger man came up to my sister and said "have the surgery & get rid of that brace". He was walking perfectly and had the knee scar to prove it.
Finally she had the surgery. Our 1st trip down from sept 2011 was March 2012. About 6 months after. She did well, but still tired easily and we had alot of rest brakes, and pool time. We focused on how she felt. If she was up to it we did it > if not we will catch it another time. It was actually great therapy for her. We did therapy in the contempary's pool and used the hot as an alternative.
Her next trip was aug. 2012 and she was 100% improved from the trip before. Her stamina was longer, I even had trouble keeping up with her.
Yes rest, yes when sitting put up your feet up, and yes we iced her knees [other one is getting done next year]. Still did alot of exercises and walking in the pool and hot tub exercises.
FYI: she has alot of allergies, so pain meds where always used at a minumun. She did not medicate while on vacation at all. With the exception of advil.
Her worse part of the trip > hauling through the airports.
I encourage you to go. Just keep in mind, it might not be your typical trip.
Remember any day at disney is a better day in itself.
Good luck and DO YOUR THERAPY!