My toothbrush is bigger than the hole of the wall mounted toothbrush holder installed in my bathroom. So I made a quick adapter.
Basically you insert the adapter peg side down through the hole in the wall holder. You place the peg on the bottom to keep it in place. Next the arms will grip the toothbrush. It seems to be holding quite well. The ones on the left in the picture are "failed" prototypes.

Most print settings shouldn't matter. If it starts getting too flexible increase the infill % That was my issue with a previous one. I went in and redesigned a little to make the arms thicker so they will spring back instead of fold