Sure, you can try. Back before there were many sophisticated smart thermostats, there were a number of both official and Community created smart apps that did just that: take existing sensors and then average use them to change the temperature on a basic zwave thermostat.
The problem almost always turned out to be accuracy. It’s not at all uncommon for the built-in temperature sensor in an inexpensive motion sensor or contact sensor to have a plus/minus of 5° . Meaning if it said the room was 68° it might actually be anywhere from 63° to 73°. Pretty useless for a thermostat.
Moderate range devices usually have a plus minus of 2°, but that’s still anywhere from 66° to 70°. The built in temperature sensor is good enough to let you know if it’s really cold or really hot, but not usually good enough for thermostat adjustments.
In contrast, both the temperature reading built into the thermostat and the sensors specifically designed for thermostat control tend to be much more accurate. For example, the ecobee remote sensors have a plus/-minus of 1°. And at my house they seem to be closer to 0.5, at least most of the time
We use an ecobee lite. We got it on sale for about $140 with two remote sensors included. Then our utility company gave us an additional $50 rebate once it was installed. So at that price it was very competitive with any of the more basic smart thermostats. It does typically list at about $100 higher with two sensors, But if you can wait for a sale you can save quite a bit. You can also save if you only want one remote sensor.
The main difference between the “LITE” model and the regular model is that with the regular model if you want you can add wired control of HVAC “accessories” like humidifiers and vents.
We chose the ecobee over the nest for a couple of reasons, but The main ones were that we also wanted HomeKit integration and we wanted a touchscreen, not a dial. But lots of people love the nest. Choice is good.
If you like super in-depth reviews, The following site is good:
So it’s up to you. But at least check the specified accuracy for any temperature sensors you intend to use for this purpose. Anything more than plus/minus 1° probably won’t work well for thermostat control.