@aizukanne shares the PCB design for a LoRa MCU board powered by an ESP32-WROVER-B with the RFM95W module. The design has an onboard 868MHz antenna with 5dBi gain. Tested and works perfectly with TTN.
The board is designed with a 24Pin Header to allow sensor modules designed specifically for this board to be plugged on as daughter-boards. So you can design your on sensor board and attach to this. Daughter boards can either take power from the 3.3V pins or provide power from the 5V pins.
Firmware can be Arduino, Micropython or mongoose OS.