Before I start monkeying with this, the thermostat is a model

CT50A4775, Class 2, 30 V max. Two wires R and W.

Do I have the right model for a gravity fed, hot water system with a gas-fired boiler? There are two wires.

My old thermostat was a honeywell (round) with a thermometer to measure room temp. and a dial.

The new Honeywell seems to have only on and off.

Maybe I need a different thermostat. I want to know the room temperature and I want to be able to control it.

Help, please, before I do something I might regret.