I cut out a piece of perfboard to fit into an enclocure that is comfortable to hold in one hand, added mounting holes, decided where the buttons should be and drilled holes for them into the enclosure:The buttons will be through-hole devices, but mounted on the soldering side. That allows me to put the microcontroller and all support circuitry on the other side and when I push the buttons, their solder joints are pushed into the PCB instead of being pulled out (I've made bad experience with that).

(The image should be upright...)