An irreverant/fantasy show with sypathetic well-intentioned protagonists, at minimum understandable volume, with characters and plotlines that invite analysis. Something about the pointlessness of studying a fantasy universe is a quite effective sleep aid. Various Star Trek series, Futurama, X-Files, Grimm, Family Guy...
For shows that are a great fit except for a few segments (boisterous theme songs, jarring fight scenes, etc) the PotPlayer Skip Playback function (hotkey ') is super useful. Also I have a basic script that gradually mutes the volume after 40 minutes.