Low power ARM Cortex microcontroller with good library support under PlatformIO

I’m looking for an ARM Cortex microcontroller with good low power library I can use with PlatformIO. Application is quite simple: sleep in the lowest power, wake up every 200ms, read some IOs, set some IOs and go to sleep. Doing it with RC clock is just fine. I would like to have a simple API call(s) to put uC into low power mode. I don’t want to look through the datasheet and set bits at the lowest, configuration register level.