CO2 is a normal byproduct of combustion. CO is formed when a fire doesn't get enough oxygen. Then it emits CO instead of CO2. If the room is too tight, enough O2 can be used up to cause the fire to emit CO instead of CO2. If you breathe CO, it will replace the O2 in your red blood cells. Once that happens, the cell is useless. When you lose enough of them, you die.
Stoves designed for tight mobile homes have an air source from outside so no room air is used for combustion. Those designed to sit against an outside wall might have an intake pipe around the exhaust pipe which both heats the incoming air for better combustion plus making a double wall exhaust pipe. Other types might have an air intake pipe coming through the floor from the crawlspace.
