My daughter (Valerie West) came up this design years ago, now I have just the gadget to make it for her... She keeps hair elastic around her wrist when she isn't wearing them, but they tend to cut into her skin uncomfortably. She had the idea to make a bracelet that has grooves in it to hold the hair ties in place, and a thumb-groove to make it easier to remove the ties when needed. I am including the STL for 3 sizes here, but you can also use the customiser to do whatever size you like...

There should be no need for supports to print this.