Re: Knee pads?
Try looking into different types of volleyball knee pads, those usually have the best combination of padded knee and flexible (not constricting) back. Also make sure that what you need are knee pads and not a brace.
Keep in mind that knee pads modify your seated techniques because they prop up your knees a bit, affecting your balance point. Despite this I use them to protect my knees when practicing seated techniques on wooden floors (I don't use them when training on mats).