I couldn't sleep for decades until I started listening to audiobooks. It's a bedtime story. Shut your mind off, let go of stress and just listen. It can still take a little while but now I fall asleep in minutes instead of 3 hours. It also helps me go back to sleep if I wake up from nightmares.
For me, podcasts specifically about going to sleep to them trigger my contrariness too much to be actually relaxing. It's gotta be on a normal topic that is just the right balance of interesting, but not exiting/engaging.
History typically scratches that itch for me. Dan Carlin's hardcore history and the history of the English being the two goats that coke immediately to mind. Camp Monsters is also a great one; the rare fiction podcast that I can actually stand, much less relaxes me enough to sleep.
I know a lot of people for which this works great. Personally though, it has the opposite effect. I cannot shut my mind of by listing to audiobooks. Either I ignore them and it's just noise, or I listen to them and stay awake until the audiobook stops.