Riding bare back also helps alot, as it stregthens your legs and helps you feel the whole movement of the horse. That or just ride without striupps for a while. Both of these exercises make you use your legs and hips.
When riding with out a saddle or without stirupps, be sure to NOT clentch on with your knees. Just let your hips absorb the movement, and be sure not to accidentally kick the horse with you loose feet. Try to keep your heels as far down as they can go without any pain. When you're an expert at that at the walk try the trot sitting, not posting. (you can do it without stirrups but it's kinda hard lol!) And see how to do!
This should help you find and keep your balance on your horse. I really hope that this information helped! I hope you're ankeles heel up! And you continue your riding carrer!