Hello,
Basically I would recommend you to use The Ultimate Relay Driver II along with some small ARexx scripts capable of turning on and off the relays via TURD's ARexx port, a Cron-like program (CyberCron would do the job) if you want to automatically call these scripts at certain hours and a (homemade) program capable of linking the Amiga and the temperature probe and read its analog value.
Anyway I don't recommend to use two-wire thermistor (PT-100, NTC, PTC or whatever) specially when long lenghts of cable are needed. Three or four-wire sensors are mandatory to deliver an accurate reading of the resistor value, but (in the case of three-wire ones) you should use both potentiometers to do this. One would read the ohmic value due to length, cross section and material of the wires, while the other would read the total ohmic value (cables + sensor). Substracting the first value from the second would deliver you the corrected (real) value of the resistor. Anyway I don't know any software for Amiga capable of doing this off the shelf, that is why I said "a homemade program" above.
Keep in mind the resistors of the Amiga are of 470 KOhm (+-10%) value.
But honestly, apart from experimenting purposes, I won't use the Amiga for such monotonous task. I would go for a inexpensive 220V/110V-powered programmable relay with analog input and RTC such as Schneider Zelio, Siemens Logo!, Omron Zen or similar that would do the job perfectly.