I sit on a swiss ball because I'm pregnant and it helps my low back and hips feel some sore of relief.
In regards to the BOSU, dome down is much harder than dome up. Here are a few exercises I enjoy. You may find them on you tube, but I'm not sure.
Dome Up:
Crunches
Side lunges
Repeater knees
Squats
Push ups
Mountain Climbers
Caterpillars across the ground ( push up, lift BOSU over head, step, put BOSU down, push up, repeat)
Dome Down:
Anything with hand weights (biceps, triceps, etc.)
Toe Touches (alternate arm/ alternate toe/ opposite leg extended)
Simply balancing on one leg