My house's furnace is a disconnected heap of rust in the crawl space, has been ever since I moved here 30+ years ago when I moved in as renter. I bought the house ~15 years ago. A central heating system is a future project.
Right now, winter is coming in, it's almost here, the thermometers tell me. When I came down this morning the kitchen thermometer said 53 F.
I have three gas burners on on my old stove and I'm computing right now on the laptop on the kitchen table. Thermometer now says 57 F, feels relatively toasty!

By the looks, there was a venting system in the kitchen, but it's closed off. I've done this for years, TBH.
Is this unhealthy?
Is the oven portion gas or electric? My furnace went out a few weeks ago & I couldn't get anyone to come in for over a week, so temporarily I left the electric oven's door open in the mornings to get things going because it's been
frigid here. Some options:
1. If it's just you, buy an electric blanket & wrap yourself in it.
2. Buy a foam toilet seat. It's like heavy-duty styrofoam or something. Not freezing when you sit on it. They don't last long-term, but they're reasonably cheap & easy to replace.
3. Buy an electric space heater. I have a simple plug-in ceramic heater with a fan. It does well in small rooms if you shut the door & give it some time to heat up the room. Based on your post above, sounds like you're already going this route for now.
4. Look at cheaper options for a furnace. I just had a Goodman installed (80% efficiency, you can do like 90/96% but you need extra piping for exhaust), not the best brand but it was readily available & far cheaper than the competitors. Already had the ductwork in place; my previous 30+ year-old furnace died. Most places quoted $3,500 to $4,000 to install, but I found a local shop willing to do cash-up-front for $2,800 (hardware + installation). Killed my budget, but at least my house isn't 40F anymore lol. Some oil/gas companies let you do a payment plan over time along with your fuel bill, but that wasn't available in my area - but if it's available in yours, then you'd have a larger monthly bill but not have to shell out a huge amount up-front.
5. My buddy has a wood-burning stove in his house. It's awesome. Nice air feel & great smell. Downside is you have to constantly load it up with wood & have a wood pile to run it. A great brand is
Jotul.
6. Another one of my buddies just got a pellet stove for his house. You have to get a delivery of pellets, but like wood, it smells nice & gives the air a nice quality. I had to get a whole-house humidifier installed along with my gas furnace because we were waking up with cracked lips & bloody noses (depends on your house layout, insulation, etc. as to whether or not that will happen with a gas furnace, from the dry air).
7. If you're mostly in just one room, you can do a mini-split HVAC system. About $2k installed per unit. Best unit I know of is the Mitsubishi Mr. Slim H2i, which has a small outdoor piece & then an indoor piece. Connects via a 3" copper tube. It does heat (can pull heat from down to -13F outside) PLUS does A/C from a single unit (and has a remote control!). Downside is that's the price for one room; my buddy did 4 units in his place because he caretakes for his parents, so there's one per bedroom plus one in the main living area. But if you're mostly in one room, two grand will get you heat & air conditioning and be reasonably efficient, which is nice.
8. Could always go the hippie route and build a DIY cob oven to heat the house: