How tf are y'all keeping your apartments warm?

My rental apartment has two huge wood-burning fireplaces that were intended to be the source of heat. It has electric wall heaters retrofitted. When I moved in, I set them all to 62F....and my PG&E bill was $550.

Any tips on staying warmer? Been using sweaters, heaters only in the rooms I'm in, beefier weatherstripping, heat pads, tea, etc.

EDIT: Responsding to some common comments below, thanks everyone!

• My apartment is pretty big, ~1500sqft, built in the 1920s. Double-paned windows, but otherwise mostly original.
• Ambient tempurature this morning in my living room was 53F. Granted, thats with no heat running since last evening.
• We aren't allowed to actually use the fireplaces anyway, so I'll look into if I can close the flues or block them.
• Yes, $550 was insane. It was ALL from the electric heaters. If I don't run them at all, the bill is like $50. Thats what electic heating gets you :( (last place had central gas, one before that had steam radiators). beefier weatherstripping, heat pads, tea, etc.

EDIT #2: Thanks for all the suggestions! There's a bunch of great things to try here, and its comforting to not be the only one excessively bundled up while inside. Stay warm!