Moes seems around the cheapest wall thermostat with wifi, but what do you want to control.
For myself when we go out for the heating to switch off, and then switch on again when we approach home switch on again would save fuel, and no need for it to be a thermostat, it could be simple on/off. Called geofencing.
However I just use a smart socket adaptor to switch my AC on/off so could use a sonoff switch without any temperature control.
What do you want it for?