Those new no-knot hairnets work great! They take some time to get used to, but I've found it very helpful in controlling my long and thick hair.
I put a hairnet on with my hair down and put it into a low ponytail , securing the main part on your head and leaving a little bubble with the ponytail. I then tuck the ponytail into that bubble and flatten it out, which usually keeps it from creating pressure points. I do sometimes have to adjust the part right around the back of the helmet or it gets uncomfortable after a few hours, but I've found that this way keeps it in the best.
I don't know what kind of hair net you use but I use the tube kind and it REALLY helps me! My hair would literally fall out of my helmet! When you put your helmet on have someone help you
I have a lot of hair, too, and I gave up years ago on trying to stuff it all under my helmet. First I tried a bigger helmet and that didn't help, so now I use two hair nets, tons of bobby pins, and put it all in a bun.
Additionally, if I'm showing during summer when it's hot, I soak my hair before the show and put it all up while it's still wet so it dries in place and somewhat flatter than usual.
A bigger helmet may cause you to injure yourself if you fall... 😳
There are hairnets kind of like ones you wear under a wig that keep all your hair together.
If you can have some sticking out, a dressage hair net and bun keep everything in place.
Honestly, i hate hair nets. espesially if its just a lesson and not a big deal, i just bend over, have my hair lose and i stuff my hair into the helemt and tuck the extra hairs away. sorry if this isnt helpful! this is what i do.