I've lived in apartments and not had the money to afford winter heating. I only ever turned it on if I was afraid the pipes would freeze and it was under -15 Fahrenheit or -26 Celsius. If the pipes freeze, I'd be breaking my lease and could get sued or evicted. So use the heating when you need to. Stay safe and take care of things and yourself the best you can.
I'd suggest the following:
When you make up your bed, layer it this way:
Fitted sheet, then a sheet that goes on top of you, then a blanket. Then a winter quilt or two summer quilts. With an extra blanket at the foot of your bed under the quilts for feet area if needed. It's the right amount of insulation and kinds of layers and so you don't sweat if too hot. .
If you have old windows. Tape plastic wrap tightly around the windows on the frame and use a hair dryer on the plastic to make it tighter. It helps Insulate things a bit better.
Wear a wool hat to bed, or something with a hood.
A space heater is nice.
Slippers and good socks by your bed and very warm long robe to put on when you get up helps, and for after showers because cold plus wet is the worse combination.