hi! also i want to control temparature of my soldering iron.....
what kind of sensor do you suggest...+- 15 (or a bit more) degree error is acceptable............and its cost should't be very much....
usually the soldering iron has a built-in probe, a thermocouple, that gives a voltage based on tip's temperature. you may try to use a spms to drive the iron, based on that voltage (tl494, uuc3842)