Tried my hand at making a fidget from scratch. Started with a 1" steel ball and modeled around it to create a thumb roller that is satisfying to hold for my hand. It may be a bit large for tiny hands but I think it is effective either way.

Printed with Sunlu PLA, used adaptive layering to really smooth out the edges. I would recommend using a brim as I had the first one fall over prior to finishing the print. Feel free to change it as you see fit.

Bought 1" Inch Precision Chrome Steel Bearing Balls G25 off of Amazon that seem to work great as the roller.