Bart said..
I use an off the shelf CTI brace and am very happy with it. I was lucky that the off the shelf was an excellent fit. They are expensive though. They allow basically no side to side movement and you can restrict your flexion and extension as needed. I've been using mine in salt water for several years now, just rinse it off with fresh and its still good.
I like the Donjoy armor, don't even need it any more but im just so used to wearing it. Had exactly the same OP and im pretty sure i would have injured the OP knee without it. Kite strappless surfboards but still reckon the brace is worth it