From my side, I can say couple of things.

1. If the temp resolution (and consistency) IS NOT very critical, then you can use LM35 with 12F675, and if only turn ON/OFF is on the subject (no voltage control) then you can directly fire the triac from PIC pin using zero-crossing.

2. If temp resolution (and consistency) is critical then you can use DS18B20 with 12F675 and fire the triac from PIC pin using zero-crossing. You can check the "busy" feature so that you do not wait for temp conversation.

In both cases, sensitive gate triacs will be more suitable for PIC's current sink (25mA max).
If you use regular triacs, then gate will draw about 35mA, thus a MOC type will be appropriate as Alain mentioned.