I'm hoping for something that can be done at home with no fancy equipment, if possible.
My physiotherapist has recommended standing unsupported (but between two strategically-placed chair backs to grab when necessary) with one foot directly in front of the other for as long as possible, and then swopping the front foot to the back and trying again. How long is "possible" varies from day to day, and according to which foot is in front, from no seconds to about 20 But in spite of doing this most days my general balance is getting worse.
In the (council run) gym where I have now been sent, they once tried me out on a wobbly semi-inflated rubber cushion, but I could never get both feet, or any of my weight, on to it. My hands soon became tired from desperately gripping the window sill, so we gave up that exercise.