With the current chilly weather, I'm mulling over the best (most
efficient) way to keep my place warm.

It will probably be more efficient to let it drop overnight, particularly as
your maisonette probably has low thermal mass. However, the difference might
not be all that great.

You really should install TRVs on all the radiators not in the thermostated
room. They could save you a lot of cash AND make you more comfortable as it
will prevent rooms overheating. It will also considerably reduce the
overshoot when heating from cold.

Christian.