There are logs that you can install in an existing fireplace and that will work without a vent. But they are controversial, because they are considered unsafe. Consumer Reports on their website has an explanation, and it is (or was) available free. You should check with your local municipality to find out if the codes allow such an installation. Many do not, especially in a sleeping room because of the threat of asfixiation.

The optimal gas logs system is direct vent, which is sealed and does not affect indoor air quality and is highly energy efficient. Such systems are essentially a firebox installed inside your existing firebox, and they are costly, at least $2K.