[noch]

> Does anyone know of a good solution for seamlessly switching between audiobooks and ebooks for books that are not bought from Amazon on Kindle?

Use Calibre's e-book viewer[^0] which uses Piper for text-to-speech.

[^0]: https://manual.calibre-ebook.com/viewer.html#read-aloud

[dewey]

Thanks, but clarification: I meant on iOS / mobile devices as I'm not reading on my computer. On second thought, it would be an amazing feature for https://prologue.audio, which is a beautiful app and works very well for audiobooks already.

[SamBorick]

ReadEra Pro is an ereader app with a decent text-to-speech, I often flip between reading and listening.