3 kids, 1 electric toothbrush and a small bathroom. That is a recipe for disaster. Let me start by telling you how much I dislike pedestal sinks or any bathroom sink without ample counter space. with 3 kids sharing a bathroom and then constantly knocking the heads off the counter and often into the toilet I know I had to come up with a solution before I spent a fortune on brush heads!
My Robo R2, and Fusion 360 to the rescue!

Using my digital calipers I measured the width of the base of the brush heads, gave myself a mm of padding around that, then
some more space for the walls of the holder, pulled it up to the height I wanted, drew a hole and then used the Pattern tool to replicate 6 holes total before cutting them down far enough that they would not fall out on their own. I added some wings to the sides to hold the suction cups (getting great use out of these!) and then printed it all in black PETG I had (didn’t need the thermal stability on these, but the structural strength works well with the suction cup clips.
An hour or so to print and I was able to snap in the suction cups and stick \it to the mirror. Not a single dropped toothbrush head since!
You can download the files from my Thingiverse page.