I generally recommend Aria the Masterpiece since it has full furigana and is on the easier side. It has sci-fi / fantasy elements, but is mostly slice of life. You may want to get about halfway through the N4 grammar points before starting, but as long as you’re willing to stop and look up unknown grammar points as you go, that should be enough to give it a shot. We also have an old book club for Aria, where some of your questions may already be answered, and if they’re not you can ask and many of us are still around to answer.
Another good option if you prefer romance stories is やがて君になる. It also has full furigana and is probably about the same difficulty as Aria. Personally, it’s one of my favorite series. It seems like maybe there was also a book club for this (incomplete though?), but since I didn’t read it with the book club I don’t know how thorough their grammar discussions were. Either way, I’m sure you could ask for help somewhere on the forums and people will respond.