Drayton by Schneider Electric Multi-Zone Smart Thermostat and 2 Smart Radiator Thermostat Kit - Combination Boilers Only - Heating Control
https://amzn.eu/d/g7aV9Dm
I installed this system a couple of years back... Managed to get it pretty cheap in a black Friday deal. If you can find the wiring diagram for your existing controller it's pretty simple swapping the connections out.
Reduced our gas bill by about a third... Which means it's paid for itself many times by now.
I've added extra thermostats on for different rooms.
Works for us as our house doesn't retain heat well and my wife works from home. We are only heating one room during the day and can warm up different places at different times of the day. Just the bedrooms for an hour in the morning etc.
The only annoying thing about it is the thermostats on the radiators are on batteries so they'll need changing every so often, but never at the same time.
Well worth the investment for us