I think you can get away with high tin solder because it doesn't tarnish that fast, or maybe not at all.
Like this
I have old circuits with high lead solder that is decades old and it has gone grey.
Yeah gold is the go.
I vaguely remember watching a fab video and you specify whether you want the gold added on top, but that applies to the whole PCB because it's done by electro-plating, so that's probably an extra. You can even get hard gold for sliding contacts.