Any charcoal will do honestly. Pick a brand that is reputable to ensure there're no unnecessary additives and carbon content is up there with the international standards.
It's a matter of quantity though. I'd estimate that in around 9 cubic meters of volume 4-5 kg of charcoal is needed. More than that will produce too much heat that might become unbearable.
Ensure burning all the charcoal at the same time to avoid different CO production rates and ensure you burn them evenly. You move the burning coals when they're glowing red and emit little to no smoke. They'll be very hot and the enclosed room temperature gets elevated too quickly so be wary of that.
Once you bring the containers inside the room, you don't have to wait outside in order for CO to rise up first. You go inside immediately and just sit or lie down comfortably. You will get the dizziness gradually and become very sleepy. I'd suggest doing this when your natural sleeping cycle is kicking in. This will hasten the sleeping process a lot.
Unless somehow you wake up from this and not die, you won't even realize anything, not even the process of falling asleep, it's that silent. But, if you do wake up, expect intense headaches, vomiting, paralysis of the lower body, severe lack of energy even for simple movements, terrible vertigo, metallic sounds in the ear and hearing muffling, severe dehydration, chest tightness with a burning feeling, racing heart and the sense of impending doom.
On top of the symptoms mentioned above, there're also risks of severe, multiple organ damage syndrome, including the brain. Long term outcomes are very random if surviving that severe poisoning. Although, if you somehow wake up and not die, expect that the symptoms will subside eventually with oxygen treatment. The chance to wake up from severe poisoning is too low but still there. That's when things become too complicated and blurry in terms of long term outcomes of survival.
This is the most peaceful death one can imagine if doing everything correctly and you don't wake up. If you don't wake up, you won't feel anything, eons shall pass and your sensing will be zero. I woke up from 12 hours of deep sleep or induced coma it brought. Couldn't even comprehend how much time I was unconscious. It was momentary falling asleep and waking up from my perspective, although 12 hours have been passed in reality. That's how silent it is.