Cemspec, you're definitely better off grabbing a thermostat. I know it's difficult to justify spending the $130 odd dollars, but it will definitely give you peace of mind. Don't even think about not getting one.
I just purchased some stuff from
http://www.wehaveitall.com.au and I have to say it was a worthwhile investment. I'd stick to microclimate for both the heatmat and the thermostat.
