What novels (not manga) could i start reading to learn grammar?

Flying Witch is a series I like a lot (the beginner club has read some of it, so you could look at the thread there). The grammar is pretty simple but a couple of the characters use tsugaru dialect, which can be tough to read – fortunately it doesn’t happen often and when it does, the joke is that the main character can’t understand them either.

Yuru Camp is good, but doesn’t have furigana – fortunately the beginner book club is starting to read it pretty soon, and it has a vocabulary list.

Yotsuba&! is a common recommendation for new readers (it was my first manga). There’s a reading club devoted to that series so I’m sure you could find a lot of good info in there.