Hi,
i put my additional files on github: GitHub - pentabarf/mbed-L011K4: custom board files for STM32L011K4
you have to copy them to the root of your mbed project.
i think i modified them to my purpose, maybe you have to do some changes to PinNames.h
But keep in mind, that mbed-os - even the bare-metal configuration (which is enabled in this files) - will take a lot of your Flash and RAM and there is not much space for your application. Thats why i stopped development with mbed for this platform and swichted to stm32cubeIDE