Sort the central heating as it's far far cheaper than using oil filled or anything else electric.
We have an old flat with super high ceilings, hugeee windows (all single glazed) and floorboards.
It's warm. I don't know why - maybe protected from the prevailing wind? but it seems to hold the heat ok once it's warm.
what we have done is put thick, heavy curtains on all the windows, all lined, velvet ones are great (old velvet - look on ebay, modern stuff isn't as thick) which was an outlay but well worth it.
large old woollen rugs on the floors that have no carpet, and also on the ones that do as carpet is quite thin.
door curtains, as well, make a big difference.
I keep the thermostat on about 18 or maybe 20 when it's like this.
We have 15 rads, only three were working when we arrived, soon sorted with a flush through of the system and only two needed to be replaced. New boiler, just a cheap one, was much cheaper to run than the old thing.