ISO Recommendations for toys for beginners

I told my girlfriend about my ballbusting fetish, and she's been ok lightly slapping my balls or flicking my balls, but it's turning her on more lately, she's been teasing about kicking (though we haven't done it yet), and thought it would be hot to use a toy on my balls.

Neither of us have any experience with this, so wondering what you'd recommend we get as a sexy toy she can use to hit my balls.