Help me choose the communication protocols that I need
As a controls engineer in the automated assembly business, I recommend IO-Link. It's had an explosion of popularity in recent years and is still growing. 


  The data size is 3 bytes.


IO-Link supports up to 32 bytes (bi-directional)


  Because the environment in which the sensor is located is harsh ( high temperature and high humidity ) the sensor has a watertight enclosure, and I can't afford to have more than 1 cable coming out of it.


IO-Link uses industry standard (usually M12) cables and field wireables which are available with high protection ratings. It can provide power and data transfer on as few as three wires in a single cable.


  I want to offer the possibility of connecting the sensor to a PLC, PC ... at the same time. 


This is what IO-Link was built for. A number of manufacturers (Balluff, IFM, Phoenix Contact, and Turk to name a few) provide IO-Link masters that handle the connection to industrial networks. This allows a PLC and PC to communicate with your sensor at the same time. 

The communication can occur in real time so a connected PLC can make instant decisions and even send commands to the sensor.