Adaptors are normally pretty useless
As a fellow member of society not blessed with stereo hearing I have been trying to find solutions for this over the years.
Most adaptors simply tie the L and R together but this never seems to work quite right in that the sound from the missing ear is there but only just (Bohemian Rhapsody is just not the same)
Really it needs something to actively mixdown the audio in the way.
Also there is the fashion horror of having a unsightly leads and lumps from it all dangling about the place.
The best solution I found so far is stereo bluetooth headsets (proper A2DP ones) and use 'Joint Stereo' if you can, it's still not perfect but does help on tracks with heavy stereo parts.