I saw the thumb index from UTG and I thought I could make something similar and it looks like it could be useful. So I made this simple design.

If you don't know what this does it's a piece to rest your thumb of the support hand for a more comfortable grip. Oh with it you'd also know your grip is at the exact location you want.

I mostly eyeballed the dimension of the thumb rest and it turned out surprisingly good. But obviously everybody's hands are different so I can't say it would fit well with your grip.

The dimensions of the screw holes were measured from these T-nuts (amazon.com/dp/B0895GGH7C). If your screws don't fit... I supposed you could enlarge the holes with a drill bit.

For practical use I print in ASA with 0.4mm nozzle and 0.08mm layer height for the fine details.

I've oriented the exported models the way I'd print them. You'd need supports.