A good question.
Since the contacts will switch micro-amps only you will need to find one with gold plated contacts. The reason being that it will see insufficient current to 'blow' the oxidisation off the contact points for silver or plain copper contacts. This oxidisation builds over time till one day the switch contact resistance is sufficiently high that the switch appears not to close. Note switch specifications include a minimum current spec.
Gold contact switches are by definition only found in quality products, but not all quality switches have gold contacts.