I'd be very interested in what you come up with soot as I'm in a simillar position having broken my leg and torn the ligaments in my knee in march. I've only been riding again for about a month now, but I've tried several things.
First what the doctors said- tubigrip- well that wold work if the ends didn't roll and cut off the blood supply.
Then I tried something simillar to a tubigrip but with fixed ends, well that rolled too.
Then I tried a neoprene one from boots and that did a great job, but by then I'd ridden so much and unbalancedly keeping too much weight on my good knee that that one's sore too, so I got another one for that leg too.
I then tried them out cubbing and the bad knee swelled really badly and the neoprene rubbed the inside of the knee raw.
So now I'm back to riding with nothing and just being really careful what I do for a bit as it strengthens. However I'd love to find something as I'm sure it'd hurt less.
OOH also- if you don't have the springy stirrups you need to get them- I can't trot with out them- my knee seizes up and I have to be helped off, with them much less pain.