CO (carbon monoxide) is a different animal than CO2, although can be fatal in high concentrations.
Here is link with some CO2 info. I personally would not be worried about the safety concerns associated with a small bottle of gas on my room, as long as safe handling procedures are followed. If a large leak were present, you would probably hear it, and barring any voilent action to the setup, it is highly unlikely that one would "pop- up" without warning. There is a large safety factor built into compressed gas equipment. If you were the type to check on your tank daily a large leak would be readily apparent (no diffuser action, and more apparent a big ZERO on the pressure gauge). If it were a small leak it probably would not be sufficient enough to seriously contaminate a room to dangerous levels over a short peiod of time. Millions of people have natural gas and propane systems in their homes WITH leaks and are unaware, even with the "rotten egg" smell added. Far more dangerous than CO2. If all safety precautions are followed you will be A-OK. Your local gas supplier will be glad to help and assist you with any questions or concerns relating to safety with with yuor purchase. Sounds like a nice setup you have planned. Good luck!