Private star network topology on Sub-1GHz
LoRa as a physical layer will work fine in your case. You can use just the radio PHY (for example RFM95) and you don't have to implement the full LoRaWAN stack.

Some other problems to think about:


Unidirectional or bidirectional transmission (should the sensor transmit again if the base station does not confirm)?
Collision avoidance
Network capacity
Retransmissions