Almost everything here is worth fixing

Your answers describe a house losing heat through more or less every available route, heated in the most expensive way. The upside is that when this much is wrong, the cheap fixes have not been done yet — so the first hundred pounds spent will do more here than in most homes.

In order: stop the air movement, seal the loft hatch and chimney, then look at glazing. And while any of that is outstanding, warming yourself rather than the building is the single biggest lever you have tonight.