Per the start of 2025 I stopped buying ebooks from Amazon. This means trying to find other ways outside of the Kindle ecosystem to acquire ebooks, preferably without lock-in. I maintain my library using Calibre and Epubor, and use those tools to be able to manage my book files locally and to read them on any device I have, in the right file format.
I read in three languages, fiction and non-fiction, and buy 50 to 100 books per year.

There are several ways to buy ebooks outside of Amazon. All options outside Amazon use the EPUB standard, sometimes with DRM and/or water marks. These are the options I’ve used since I’ve stopped using Amazon:

Directly from authors

Various authors sell their ebooks directly from their own sites. This has the benefit that more money goes directly to them, and there will be no DRM on the files.

Cory Doctorow (sf, non-fiction)

Michael W. Lucas (sf, non-fiction)

I’ll keep adding authors I can buy directly from to this list, suggestions are welcome too.

Directly from publishers

There are publishers that directly sell from their sites.

Verso Books, a UK based self-proclaimed radical left publisher, of fiction and (mostly) non-fiction. I have a monthly subscription which gives me access to all their ebook publications. I don’t find something of my liking every month, but often enough. DRM free.

Maven Publishing, Dutch and translated into Dutch non-fiction. DRM free, I’m not sure if the books are water marked.

Standard Books, a USA based publisher of English public domain works (fiction and non-fiction), released for free and as public domain (you can make donations, I do). Public domain works in the USA may still be copyrighted elsewhere.

Reclam Verlag, German literature and non-fiction, aimed at school use. DRM free with water marks.

I’m looking for more publishers that sell their own ebooks, feedback welcome.

Other independent platforms

Some platforms that aren’t tied to specific ecosystems sell ebooks. Be aware of what type of DRM they use, and determine first if you can handle that type of DRM.

ebooks.com, a USA based seller, using Adobe DRM although the site itself suggests they have their own type too.

Beam, German platform for DRM free ebooks, with water marks. Large selection of SF. By the looks of it German language only. Only accepts account holders with addresses in Germany, Austria and Switzerland.

Libris.nl, the platform of a chain of Dutch booksellers. Adobe DRM for English books, DRM free and water marks for Dutch books. Fiction and non-fiction. You can select your preferred actual book store first, and have your purchase accrue with them. Libris collaborates with the German Tolino e-reader maker.

Morawa, Austrian chain of booksellers (since the 19th century), ebooks can have DRM, but also many with water marks. They don’t sell outside of Austria . However you can add any Austrian address, as that doesn’t affect your downloads.

From other silo’d ecosystems

Rakuten Kobo, a Japanese company, selling ebooks for their Kobo ecosystem. DRM’d (Adobe). Sometimes cheaper than the main Dutch Kobo platform (Bol.com). Sales to EU through their Irish legal entity.

Bol.com, the largest Dutch online platform for books. Part of the Kobo ecosystem. Fiction and non-fiction, Dutch and English. DRM’d for English books, DRM free and water marked for Dutch language books.

Tolino, the German e-reader manufacturer Tolino works with the German book retail sector, like e.g. the Thalia and Hugendubel chains, or non-chain bookstores like Dussmann in Berlin (although Dussmann also works with the Ukrainian/Swiss Pocketbook ereader company. Adobe DRM is in use but many works are also DRM free and water marked. It seems a German residential address needs to be added to an account at these stores before buying ebooks is possible.