My problem is I live in an old building built in Soviet times. Besides, both my rooms have outer walls and this is another drawback. They are extremely energy inefficient.

Yes ... I know about one such apartment. It was quite deep, not that much heat lost through the walls, but the windows were leaking a lot, and temperatures on the outside sometimes dropping to -30C. They replaced the windows with modern windows, and with the radiators still working on full effect (they had a "do not touch"-policy on the old radiators - try to adjust it, and it may start leaking) in addition to the heat from the apartments below and above, it got really hot in the winter time. Too hot. But luckily the windows could still be opened ...

Even before the war broke out, we were suffering from high energy prices, so I sort of made it into a sport to use as little energy as possible for heating. My friend JJ in Poland has also mostly kept his house at around 14C throughout the last parts of this winter to save on the energy. Even the price of firewood in Poland was roughly doubled between September and March.

I wrote up an article on how to save energy eventually :-)