Replacing thermistor for heater with arduino
My approach to this was simple. Get a digital pot, in this case MCP41010 10k and set it to the apropriate value for the temperature I got from some sensor.
Arduino talks SPI to the pot
The arduino is electricaly isolated from the heater exept the wiper terminal and terminal A on the digital pot which are connected to the two terminals where the thermistor would go.
If I were in your shoes, I would get a 10K linear pot and a 6 or 9g hobby servo, and connect the shafts.