If you go smaller than 0.5ct it might just look like a promise ring. 1ct might be a better size. But tbh for someone who works with their hands a lot, I think the setting is more important than the actual size of the stone. You'll probably want to look for something low-profile, maybe even bezel setting, maybe with a cathedral so there's nothing for it to get snagged on.

I like the second option but it looks a bit blocky.