Sounds right to me. So as a compromise, how about putting a wireless stat
in
the conservatory and replacing the stat in the hall with a TRV on the hall
radiator?

Whilst this would work, it has the very serious problem that the radiator in
the thermostat room shouldn't not be controllable (i.e. should have
lockshields both ends). By putting an unzoned thermostat in the
conservatory, you are basically removing the ability to turn off
conservatory heating.

OK, will some of the other solutions you don't have independent timing, but
at least you could manually control it.

Christian.