An example you can start with is the sldemo_househeat model, which models the heating logic for a simple thermal model of a house. You can find the documentation at this link.
If you look at the "Thermostat" subsystem, there is a "Relay" block which essentially turns a heater on/off based on the temperature difference between the measured and desired temperatures. This would be your "on-off" control.
The "Heater Subsystem", in a way, implements proportional control. The model seems to be that the heater air is at a controlled temperature, and the heat transfer is proportional to the temperature difference between the heater air and the house temperatures. You could likely modify this logic so your controlled variable is the amount of heat supplied by the heater, which would be a true proportional control example.