Options regarding knee braces are quite limited.
Law 4.1 (a)
A player may wear supports made of elasticated or compressible materials which must be washable.
What you cannot wear is anything with metal or rigid supports or hinges.
Law 4.4 (c)
A player must not wear any items containing buckles, clips, rings, hinges, zippers, screws, bolts or rigid material or projection not otherwise permitted under this Law.
In essence, if your knee needs more than a simple support sleeve, you are probably not ready to play yet.