What kind of sandal or shoe is recommended for ankle instability and/or arthritis?

High tops: High tops sneakers will help. Also there are custom made orthotics used to deal with ankle instability and arthritic changes of the ankle. Even though a custom orthotics may be expensive, long term you will save money. They last 5-10 years depending on the level of activity. See a podiatrist for evaluation and correct prescription for a custom made orthotics.

Depends: It depends on the cause of the disability.