Very simple but effective exercise:
Stand on one leg, eyes closed, balance upright for 5s with minimal upperbody movement, no arm-flapping etc.
once you are steady, bend your knee and go down as far as you can into a squat, then back up x5
5th dip, hold and balance at lowest point for 5s
x5 more dips, then switch legs
If you want make this more challenging, do it standing on a thick piece of memory foam, a mattress, or any other soft surface that will making balancing more difficult