Electronic switching energy regulator

If I remember correctly a Simmerstat was the predecessor of the common triac Dimmer but only used for low end domestic ovens and such.

There was a small heater and bi-metal strip which depending on the setting kept the power on more and more time. It was only suitable for ovens and other heaters due to the long on and off times and there was no thermal feedback to the simmerstat. Given that is what you need then an ordinary triac dimmer will do your job but better as long as the power rating is observed.