The number of podcasts "out there" seems to growing exponentially.
Overall, I think that this is a good development. However, like everything else, dark forces begin to ruin every good thing that comes along. In my opinion, podcasts are no exception.
You can use a search engine like
https://www.listennotes.com/ to find podcasts on subjects that you're interested in, but you're still on your own to weed out the bad ones.
I was perusing the publisher Macmillan's website (
https://us.macmillan.com/podcasts/) just now, however, and noticed that the apparent handful of podcasts that they have so far all seem to be much more dignified and substantive than the usual fare.* I encourage you to take a look!
It appears that all of the podcasts are _free_.
* I can't speak to podcasts that any of the (many) Macmillan imprints may have.