Hi Creampuff! Yeah, you've got challenges there when it comes to kayaking. My husband has bad knees and getting into a kayak is hard for him. Here are some tips, which may or may not be feasible, but let's try...
1) Get a sit-on kayak. They're easier to get on with bad knees. Con: they are not as stable in moving water.
2) Always have a kayak buddy to help you in and out. I have a friend with bad knees and I have to hold a paddle like a handle for her to pull up on.
3) To get in, while the kayak is half on solid ground, I put one foot in, lower myself to sit on the back of the cockpit while holding both sides of the cockpit with my hands. It is important to get your bum on the kayak as quickly as possible. Once the kayak starts wobbling, you have more chance of getting hurt. Then I put in my other foot and lower my bum onto the seat.
4) To get out, while the kayak is resting half on solid ground, I hold onto both sides of the cockpit and raise my bum out of the kayak to the back of the kayak cockpit. Then I turn to the side with both feet out of the kayak into the water. With both hands on the kayak, I push up. Again, the quicker you can transfer your weight onto your legs, the better. It would be good to either push the kayak against something solid, or have someone steady your kayak. I'm usually the one with good knees, so I can't usually count on my buddy for help.
5) Use your paddle to help get in and out.
6) Practice getting in and out a few times before you take off.
7) Strengthen the muscles on the inside of your knees, as well as other leg muscles to help move with confidence.
8) Use extra cushions!
9) Start easy. Don't do a river trip until you are strong. And don't do a long trip until you know how long you can sit on your hip. And make sure you are ready if your kayak flips...can you swim with your new hip, and handle your kayak, paddle, etc. And how would you reenter your kayak?
Okay, I think that's it. I hope it helps!
Happy kayaking!