A good pair of closed back headphones (that have cups that reduce the sound from the headphones from reaching the microphone) are an essential investment when you are putting together your narration setup.
Closed back headsets allow you to monitor your performance at a sound level that will enable you to hear problems or errors that can impact the quality of the record. For example, you can listen for rustling of papers, squeaky chair noises, and other glitches that would go unnoticed.
If you need to hear your voice directly, then move one of the ear cups of that ear (and if possible, lower the volume on that side using the balance control). This will end up saving you time in editing and retakes.