Since the prototype works without any issues, I went ahead and ordered a PCB from OSH-Park, to make it a little easier to knock a few more of these switches together. The board is 50mm long and 15mm high, so that it fits down the side of the battery box in the "dollar-store" LED light case that I'm using for these units. There are no mounting holes, as the board is so small and light that it can be held in place with double-sided tape or hot glue.

Be warned that (as of early Nov 2016) I haven't received the first batch of boards yet, so it's untested, but the OSH-Park shared project order is here:-