I've heard lysol with water was used a lot. Here was a post I found online:
Lysol Original liquid with the blue cap. Dilute with 3 parts water. This is a good formula as it kills most bacteria and common viruses. Plus, the odor is very pleasant.
I wouldn't clean the foam inside the covering with anything. If it wears out or gets moldy you need to replace the foam. Anything you try to clean it with will just be absorbed. If you are in a pinch they do make powder base cleaners, but they are expensive.