In looking at the personal weather station thread, it occurred to me that a Pokitto hat that let you plug in the :bit boards might be a better approach. Others interfaces might be a better choice, but the obvious choices have problems. Raspberry Pi’s expose a lot more pins, and Arduino shields a few more plus being large compared to the Pokitto.
The micro.bit seems like a good fit: it exposes 20 pins on an edge connector, and uses a Cortex M0 CPU (Nordic nRF51822).
The Adafruit Feather line might also be worth looking at; similar pin counts to the Arduino in a smaller form factor.