Regulating precision heating
What accuracy do you want for the control, for instance the peak to peak temperature excursions?

The very simplest would be to strap a bimetallic switch to the element. However, due to the time lag between the element heating and the strip heating, and the hysteresis present in the switch, you could expect possibly 10&deg;C to 20&deg;C cycling in the element temperature.

If you want tighter control of the excursion, then you would need some form of continuous sensing, with a PID control of the heat. 

My definition of 'simple' was to go onto a well known online auction site and buy a cheap PID temperature controller, for a few 10s of GBP, which takes a thermocouple input, and drives  a PWM relay output. It has worked with default tuning for every heater/load scenario I've thrown at it so far, from a sous vide water bath, to hot air ovens.

Depending on your heater, you could perhaps sense the temperature directly. Most resistors and resistance wires used in heaters have near zero tempco. However, if you can build the heater from a straight metal (iron, copper, stainless steel for example), then you can sense the resistance of the heater to control the input power. As this is very fast responding, you should be able to get relatively small excursions with a simple on/off controller. You can either sense while driving, with an asymmetric Wheatstone Bridge arrangement, or drive with PWM and measure the resistance during the 'off' times.