Depending on what level of protection you are looking for, these might do the trick. I use them and they can fit under my slim fit jeans. They are going to save you from small bumps and scrapes, but obviously a big slam would still hurt with these:

https://www.amazon.com/Triple-Covert-Knee-Black-Medium/dp/B00IS6KOYA/ref=sr\_1\_7?dchild=1&keywords=triple+8+knee+pads&qid=1628620336&sr=8-7