Ideally it would be something with a large number of sentences where one typically-kanji word was written in kana. And then the reverse side shows how to write the kanji.
And ideally these wouldn’t be learner-written sentences.
It doesn’t need to be organized by any particular difficulty. In fact, I’m trying to get away from things specifically for certain Kanken levels, etc. Just for a break.
Not what you asked but here is an idea. Get a librivox audiobook and write out the sentences as you listen, then compare them against the gutenberg text. I suppose you could make an anki deck out of that. Not sure how archaic the japanese texts there might be though.