Try searching on Honeywell RTH6580WF "c wire". That is not the brand that I have, but it seems to be be good value. I would upgrade to the one that displays the humidity myself, but you do not need it.
You will need to have a C wire to power the thermostat unless you get a separate power transformer, which you would rather not do. If your thermostat cable has more than 2 wires, you can wire the C wire yourself at your boiler controls where the other wires connect. There is a lot of discussions of C wire.