I found using the Alta knee pads really help ( https://smile.amazon.com/gp/product/B00F7FM2CM ) . For going prone I just lean back and fall onto my knees. With the Alta pads my knees don't feel it on the dirt, rocks or even concrete. To me they are comfortable and I sometimes forget I'm wearing them. At least until I try to get in the truck after the match and catch them on the bottom of the dashboard.
I dig the Alta FLEX line.
Here is a pair i got on amazon
The top strap is elastic while the bottom is not so it doesn't cut into the back of your knees. I really like them because there is no velcro and they are quick detach.
Alta Kneepads are my favorite hands down, and I’ve been through many. Even more comfortable than any crye or UFPRO. That said, any knee pad ever is prone to sliding around. Usually only a small issue, but it’s enough that I’d save up for tactical pant with built in knee pads. Of the built in knee pad pants, I like UF PRO best. Expensive in US, but good comfortable stuff.