I bought the XIAO BLE board just for this application, with addition of rain gauge bucket tips recording. By pressing a bouton, it starts a BT connexion allowing me to gather datas on a smartphone (and make configuration). I started first with the adafruit feather nrf52840 and latter with the itsybitsy. Nevertheless, power consumption was too high, around 1 mA, due to onboard neo-leds that have a high current drain even when dark.
So, I want to build a weather data logger for very remote places (oversea, cave). I want to have a working duration of 3 years. A AA LiSOCl2 battery has a capacity 2.6 Ah. With your sleep current, it is not so far.
I will follow your project carefully.