Just to add that you could always look at using the nRF52. They're pretty good on power usage, and you get Bluetooth too.
@Gordon started
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
Just to add that you could always look at using the nRF52. They're pretty good on power usage, and you get Bluetooth too.