I am using vThermostat from nclark. You specify a temperature sensor when you set up the app. The app creates a thermostat device.
In the past, I have used the built-in virtual thermostat. With that, you need a rule like the one below to get the temperature value from the temperature sensor to the virtual thermostat. Note that it is copied first to a local variable.
Virtual thermostats and my App may not solve the issue you discuss above. Your Ecobee might "outsmart" your virtual thermostats the same way it outsmarted your simple rules. On the one hand, you want the Ecobee to behave the way you expect it to. On the other hand, you want it to exercise some deeper "intelligence". Those goals may be incompatible. You can't hire a famous architect and then expect them to just draw the house you tell them to draw.
