If you want to go down the route offered by GP, buy it anywhere and then pirate the epub. The author is compensated, you get the freedom of an unconstrained ebook file, everyone wins.

For books from small and specialty presses, I like to buy the ebook from the publisher because they'll often sell you a copy without DRM. Mind you, this has been true for tech presses and small companies but not for university presses and imprints attached to big publishing houses.

Humble Bundles (if you get lucky and find a good one) are also usually just DRM-free files in a zip archive. I've seen more sci-fi bundles lately (e.g., they had bundles of the complete works of John Scalzi, V.E. Schwab, and Ursula K LeGuin last year), and I think they usually have some anime bundle on offer.

Kobo is also a pretty complete bookstore, and they tend to match a lot of the "1.99 ebook today only!" sales that Amazon runs. I do most of my reading on one of their devices becaus you can sync PDFs/ePubs (via a USB cable or Dropbox) and log in directly to Pocket (for web pages) and OverDrive (for library books).

I saw Bookshop.org also sells ebooks, but their marketing copy ("read right in your web browser, or download our iPhone or Android apps for the full reading experience") makes it sound like they built a closed platform and don't sell files.

I buy from Ebooks.com it comes with the adobe drm but it is super easy to strip using a calibre plugin

This! I did this when an relatively new but obscure book was needed for work.

Read it on my kindle after removing the DRM and sent it via amazon.com/sendtokindle

Honestly in most genres you're hosed, but if you're into Japanese nerd stuff, j-novel club sells light novels (and a few manga) with no DRM.

Wait WHAT?! I’ve been buying ebooks off BookWalker and it’s so annoying. Their reader app sucks and they have these faux-protective constraints like not permitting a “copy” function on any highlighted text and limiting a book to no more than 50 highlights. It’s so silly… Edit: damn, had assumed you meant maximum nerd mode and that these books were available in Japanese… looks like it’s all English translations. So it goes.

I've switched from Amazon to Kobo (in terms of a store, I don't use either's devices). I tested last night and I was able to copy epubs purchased from Kobo wherever I wanted. They have all of what you just described.

Like you, I insist on having the ability to archive and backup my media, and the second I learned that Amazon was removing that ability I was done with them.

Also just to echo what others have said, I'm of the belief that once you pay for a book/game/etc... as long as you're the only one using it, the rest is free game. Pirate away after you buy a copy and I don't think there's an ethical problem there.

Some of the books on the kobo store come with DRM, but if that’s the case it says so in the description.

That's true, but it's also the Adobe DRM which can be trivially stripped using Calibre, so it's not a big deal IMO.