Posture exercises. Even just sitting straight at your desk with something on your head, & when walking. And any exercise that improves core muscles, strong stomach muscles make a huge difference to balance. That doesn't mean a bikini body is vital, but the actual muscles in your stomach should be the basis of your upper body balance & position, rather than holding your back & shoulders rigidly.
The above plus a wobble board which is brilliant for core muscle strength and balance. Pilates is also good or yoga for suppleness.
I recently had a lesson on a mechanical horse in Surrey who is really good to practice on for dressage aids. After an hour, despite riding 5 times a week, I ached in places I didn't know existed the next day.