Best Book/Source for King Arthur stories and lore

I want to learn more about King Arthur’s saga, for my own enjoyment and curiosity but also so I can authentically write a short story set in that time and maybe have a character in there like Gawain or Lancelot. To get an overview I just read the illustrated Robin Lister one, which is what my library had; seemed like a kid’s book but it didn’t sanitize things and was from Merlin’s perspective, which was cool. It was pretty comprehensive but still brief. I’m looking for more details and complexity.

The challenge for me is trying to find a volume that covers everything, or at least most of it, that isn’t aimed at kids or sanitized and ideally in the public domain. I planned to get the one by Howard Pyle, but then learned it was for kids. The Buried Giant by Kazuo Ishiguro was really good, but took place a while after Arthur died and came out just 10 years ago. If I wanted to try and submit/publish what I write, beyond just doing fan fiction, I couldn’t lift any new elements/ideas from things not in the public domain, which the original medieval sources are i.e. Thomas Malory’s Le Morte d’Arthur, but I heard those are difficult to read.

Maybe a more recent book that just simplifies the writing style without changing much (Does T.H. White's Once and Future King fit this description? Or does that change things?). I want as much historical accuracy as possible but still with the fantasy elements, not like the King Arthur movie from 2004.

I read Idylls of the King back in college and could just use that if it’s a well-rounded account of everything, I don’t remember. I will try that soon. Thanks for any help you can provide!