I'm a Code Enforcement/Housing Inspector for the largest city in VT. We deal with this all the time. Many of the new building/electrical codes require the installation of hardwired smoke detectors in new construction or at the time of sale. Depends on the area you are located in and whether or not your local government has adopted the newest building or electrical code.
Sounds like your detectors are interconnected. That's a good thing. You want the detectors in your bedroom to go off at the same time as the one in the same location as the fire. Conversely if the CO detector in the basement goes off it will activate the other CO detectors in the house. Giving you time to get you and your family out. You can purchase combonation smoke and CO detectors. They cost about 75 bucks. Put one in the hallway outside your bedrooms, and one on each level of your home. The one outside your bedrooms counts as that level. Make sure that the electrician you hire to do this follows the instructions. There may be a minimum distance that the detectors need to be located from fuel burning appliances. Ceiling location is usually fine as the gas is very similar to air and warm air rises. If you are still concerened then by all means use a plug in type of co detector. Check to see if the detectors are UL 2034 listed and approved. Good luck, seems your are certainly on the right track
Matt