Zoning cast iron radiators

[Stretch5]

so in my new house i have cast iron radiators on both floors. the problem is, is that there is only one thermostat on the main floor. The main floor will be comfortable while the upstairs is sweltering. The way that they were plumbed its near impossible to set another thermostat zone upstairs without completely redoing it all. I recently talked to someone that told me about individual thermostats that replaces the inlet valve and are controlled by an actual control panel on the wall. Has any one heard of these? I tried to search for them but its hard if im not entirely sure what they are or called. thanks