You can use Nest Gen 3 or Nest e but I after fitting Nest Gen 3 am no fan of Nest. The nest temperature sensors have not been released in the UK, only US, so Nest can only sense one room.
Most the other so called 'Smart' thermostats can link to TRV heads so can sense more than one room.
Oil and old gas boilers turn on/off, modern gas boilers turn down, although there are thermostats that connect to ebus like the OpenTherm used with Nest, in the main the TRV controls room temperature and the wall thermostat is only there to stop the boiler cycling.
I do see the idea of geofencing, but there are practical problems, my Nest worked until Google took over, but have found no controls other than eco and comfort temperatures.
The whole idea is when your x miles from home, heating turns on, however what we want is x minutes, it will take a set time to raise the temperature from a holding temperature (Eco) to a running temperature (Comfort) and so one hour can be 70 miles to 5 miles depending where you live.
I have Energenie TRV heads which were claimed to work with Nest, they don't, but they have a OTT anti-hysteresis software so set to 20°C when room at 16°C and it can take 3 hours to reach 20°C, so I would set at 22°C for one hour, then 20°C and it was at 20°C in one hour. However can't do that with geofencing, so the Drayton Wiser TRV head claims to have built in algorithms which work out time taken so can rewarm the room within the hour. Not used them so don't know if that is true.
What we want is a comparison between makes of TRV head, although eQ-3 and Terrier i30 electronic heads are stand alone, most connect to a wall thermostat or hub, some are controlled from the wall unit,
others need a phone, tablet, or PC to access the system, this
looks good on the PC, but this
is so much easier, on touch of right hand button and swaps eco - comfort or comfort - eco, yes can use bluetooth
but I do not walk around at home with my mobile glued to my side.
Same applies with wall thermostat
in the main I simply turn the dial