My coach used to help me out by tying my stirrup leather to my girth! Helped my position so much!
Grip with your calf’s and not knee
I think that you just need to just push your heels down
work on two point durin the trot and canter and also do tons of no stirrup work!!
If you try to think over the jump and make your legs still, it will just become something you are used to so you won’t have to think about it anymore:) I had the same habit and this worked for me :)
What helps me is I ride in jockey stirrups for a couple weeks and as soon as I put my stirups back down my legs don’t mov