Self-publishing is the way to go. I built my own platform to sell my book Mastering Modern Payments[1] but if I were starting from scratch I would strongly consider something like Softcover.
Since launch it's made approximately $35k. Not quite the solid success that the OP talks about, but then again I invested far less time than the OP suggests.
That's really great. An extra $35k is always a good thing. I published my second book (http://wewut.com) on http://leanpub.com, and I've been really happy with the results.
Since launch it's made approximately $35k. Not quite the solid success that the OP talks about, but then again I invested far less time than the OP suggests.
[1]: https://www.petekeen.net/mastering-modern-payments