Book Authors: How do you create/generate your eBooks?

Somewhat related to the new Write.as feature that generates eBooks, but I’ve shifted to iPad only (no more Mac) and am wondering if there is anything folks are using that is more intuitive and Apple-like than PressBooks.com. I’ve looked into Calebre and it’s predecessor, and find them puzzling. (Vellum, Mac only, sets a high bar.)

Thanks,
Patrick