I’d recommend finding a rechargeable that uses a magnetic charger. The body of the egg will have two small magnetic dots where the magnetic charger attaches, allowing the egg to be waterproof and hygienic. You’ll want one with a cord, and something at the end of the cord to prevent it from going inside of you. You should put the egg in a condom with the end staying outside of your bum which helps alleviate concerns of the cord breaking.

“Vibrating Ben wa balls” is a good search term for what you’re looking for, but again, ensure the design will prevent it from being pulled entirely inside.

This option appears safe although it’s not exactly what you’re looking for: www.edenfantasys.com/…/menworks-system