I have the Tado Smart Thermostat, and my own boiler. We have one room in the flat which is colder than the rest of the flat and I would like to be able to set the temperature there separately. Consequently I'd be interested in purchasing the Smart Radiator Thermostat but I'm not sure how many I'd need. As far as I understand it, I'd actually need to purchase one for every radiator, in order to be able to set the temperature of just the one colder room. Is that correct?