I’d try 1/8 TOPS. 1/4 is overkill, and 1/2 is WAY high, not to mention expensive if you don’t know where to shop.
Sorry to hear about the malfuncition there! The separate, isolated servo-powered circuit is the way to go. You could even get a switch from radio shack you could use instead of just wires. I’d go for a lever or roller-lever switch- they look like smaller versions of the official VEX limit switches.