You want a PID and a type K thermocouple. The thermocouple should be 10 or 12 gauge. A ceramic TC sheath is also a good idea. The PID can be used as a read-only device, or made to turn on/off a control. On a forge , you could have it turn on a red light when the forge gets to the set point. Later on, you could make the forge controlled by the PID by adding a solenoid valve in the gas line. Read the PID controlled Forge sticky for more info.