This is from a few years ago, but it was a fun project, so here are some photos from building this thumb keyboard.  First thing was trying some buttons to see what felt good.  Best (subjective) feel were the top left surface mount buttons, and then probably the translucent clicker at bottom right. The clicker would be easier to mount but...

It turns out that if you space out header pins every 3rd hole on some perfboard, they perfectly fit the surface mount buttons, and by orienting the buttons diagonally, they can be soldered in one at a time without blocking each others pins from soldering.

And the longer ends of  the pins sticking through the back of the board are perfect for soldering diodes and wires to.