Mouse Creation

Hi, I am slowly gotten more interested in mouses over this year. Today in the shower, I decided I would make my own mouse from scratch. I have no idea how I should go about making it. (I was thinking about potentially selling it as a side business). I was thinking about using resin printers and learn CAD over summer to better design the mouse. Does anyone know how I should start and how I should get custom shaped PCBs and mouse software? Thank you so much, please guide me!