I have a couple of games with the 120v doors. I was concerned about that voltage but took a much simpler approach,

I added a plastic insulating strip on top of the fishpaper to double insulate it. I mounted small piece of plastic between the leaf switch and the back side of the door and I 3d printed a new plastic button to replace the metal one.

So there is no way for the switch, the wires or the solder tabs to touch anything metal on the coin door. It still has 120 volts at the door but I'm not worried about it shorting to the door and causing a shock.

I added the plastic insulation because the fishpaper was worn almost all the way through on the end. You could see light through it. That fishpaper was the only thing between the button and 120 volts. While I had it apart I used the same plastic to isolate the entire switch from the metal door.

Once that fishpaper wore through, a GFCI might protect you from a shock but you can't play a game that trips a GFCI every time you start it.