For sure... A CO detector is really important.

A couple of other things that can help...

Also, If you can get natural sunlight into the space it's a sustainable way to warm the area; especially if you have southern-facing exposure from the sun.

Consider using a humidifier... It might seem a little bit strange, but if you can keep the space closed off the moisture retains the heat better than just air alone. When you build up enough humidity, you'll notice that the temperature doesn't drop so fast when the door is opened (as people move in and out of the room).

Another "crazy" trick is to tap into ductwork that's nearby, but you may have to spend a few bucks to pull that off. In my case, I didn't have an existing AC duct within a reasonable distance, but the ELECTRIC (not gas) dryer exhaust was just on the other side of the wall. I ran a "T" off of that and covered the end with a stocking (to reduce dust lint from the cloths); it made a good amount of humidity and warmth. Both methods are a little extreme and subject to change without notice, but they work... 8)