Post below has corrections and missed information please take the time to consider Intoxicated post. It is after this one.
CO chemical generator. All items at a local store, nothing restricted. Get a 2 gallon wide mouth mason jar and a half pint jar put sulphuric acid in big jar and put Formic acid in small jar put small jar inside big jar. Sulphuric acid doesn't go over small jar height. Get a cap drill a hole in it. Run fish tank tubing in the hole just a half
Inch, silicone it up around the tube. Place other end of tube inside a 5 gallon bucket filled half way with water, use silicon after drilling hole in 5 gallon bucket lid, use a dab of silicone to stick tube to bottom of bucket. Drill a second hole in bucket lid, this tube maybe an inch in, silicone that tube in lid. Seal lid on to bucket after water inside. Get a regular oxygen medical mask, put on face.
Go back to big mason jar lean it on its side at an angle, make sure the little jar mixes with the sulphuric acid in big jar. Wait maybe 15 to 30 secs and put in mask.
The big bucket is a chemical wash, gets rid of any residual sulphuric acid as it passes through the water. CO builds up on top half of 5 gallons bucket and gets passed to the mask.
I would do 3 chemical generators connected to the 5 gallon bucket. CO generators put off a lot of CO.
The whole setup less than 100$ at a local store. The sulphuric acid is drain cleaner can always find one brand with that on the label same in formic, when you look for it won't be much.
For me was the most peaceful, cheapest, non screw up way to go by inert gas. Anything you want to do to ensure a better deal is all you. Once the generators are going and with a good seal on a front face mask I would guess less than 10 minutes for consciousness and given mask stayed attached death soon to follow.
So that is a CO option without charcoal.