Cheers for all the help guys! I've gone ahead and bought another thermostat and smaller heat mat. I'll run the warm side through the pulse proportional thermostat and the cold side through the simple on/off switching thermostat, I'm sure this should keep temps pretty constant! I considered a dimmer but not being home all the time to constantly adjust it encouraged me to spend a bit more and invest in another thermostat (not much more thanks to ebay!!). Perfect temps in a few days hopefully!!
Thanks again!