We do that too! I can do 4 laps in walk before I die, 6 in trot, and 2 in canter... I'm getting there lol.
We also do this: take your feet out the stirrups, and relax them for a moment, then bring you knees up so that they are by your ears basically, and keep your entire leg away from the saddle. Also try and sit up straight... It's **** funny to watch, and we always groan, but it helps us sit deeper, helps with balance, and makes us look like complete ******s
We also lay forwards and backwards, as far as we can, while keeping our leg dead still, that has helped a lot with jumping. We also touch our toes, right to left, left to right etc, at walk and trot, and that really helps with balance.
It all helps, but your legs feel like jelly afterwards