Gas heaters can produce CO if they’re not working correctly. Best to not use one at all. Just get a wood stove.
Decades ago, a woman and I woke up with really bad headaches after the first night that winter that was cold enough to kick the gas heater on. The repairman who looked at it said that the heater manifold was cracked and that we were lucky to wake up at all.
My BIL died this way when he was in college. Heater in his apartment went bad.