Hi young man, well you are younger than me.
I have been looking at cars for under 25 so my offspring can drive for me. The choice is limited for me. I have come across an ideal car. It’s the seat ateca xcellence lux 1.6 diesel. The only engine available for under 25s. You could opt for a petrol engine which is more powerful and a different spec. Why this spec? Well it has all round parking camera and reversing camera. It has park assist. Great for the kids not to bump into anything. I have difficulty lifting my left leg. The sill is at the correct height and it is easy to get in and out. You mentioned issues with your right knee, you might struggle getting out a lower height car. I might recommend that you go for an auto since you have limited movements in your arm. The bonus point for me was the height adjustable passenger seat. By the way it has a feature which applies the brakes if you get too close to a car in front etc.
This is one choice for you. Your first step is to go to any local dealer and decide what size height car is suitable for you then fine tune your selection.