I feel for your knee pain.
I also had a knee problem which actually stopped me using stilts and walk but gladly got rid of it threw stretching and physiotherapy and now I have to wear inserts to push my knee in place.
but if you want to convince your parents the best just say "buy me stilts or ill dump you as my parent"
(if you actually do this then I didn't tell you to do it)
P.s. probably a bad idea