Body-weight squats/air squats are a great option that can be added into a regular exercise routine. There are many variations to this form of squat, but using a Bosu ball can take this exercise to another level. The squats can be performed the same, but the instability of the Bosu ball forces more muscle engagement form the legs and core in order to maintain balance.
The Bosu ball can also be used from either side for both double and single leg exercises. Considering the added instability, the movements should be done slow and controlled for safety and to avoid the chance of injury.