Check into Ecobee but I think the problem you run into is that the remote sensors are made for rooms other than the room the primary T-stat is in, so if you are in the cold room it will warm up the rest of the house to match your cold room if you are in it.
Not sure what "problem" you're describing. You get one thing to control per zone. That's how zones work. One Ecobee, one zone, one input to the furnace. The Ecobee remote sensors allow you to balance the temperature across multiple areas in the same zone, but it's still just one thermostat.
In my case, I have a central hallway upstairs with a window and radiator, and bedrooms around it, with a thermostat. On cold nights, heat from the downstairs zone would rise up the staircase and warm the hallway, heating the thermostat, which would leave the bedrooms cold.
With the Ecobee, I have sensors in three bedrooms and turned off the internal sensor as an input, so now I balance the bedroom temperatures and let the hallway float. Placing the thermostat in a single bedroom would not work as well, as different conditions can cause each one to be warmer or cooler than the others, so having multiple sensors strikes a better balance. Of course, the best balance would be with zones in each room, but that would be difficult to do at this point.
Anyway, be sure that whatever you get with external sensors allows you to disable the internal sensor's input too.
