Adding hot water control

I bought a Smart Thermostat Starter Kit - v3 and several smart radiator thermostats back in 2018. It's worked well for the heating but we've never been able to control the hot water separately from the heating as we don't have a three way valve to enable that. However, we're now looking into getting a completely new tank system with an air source heat pump and this will allow us to control them separately. My question is how can I upgrade my V3 system to do this? And as well as buying whatever is needed, will I need to start paying monthly, something I don't need to do now?

Thanks.