Harder Kinder Books

My son has always lovvvved books. We’re nearing the end of kindergarten and he is now full on reading independently. It’s like a flip switched over night. I keep throwing harder things to read at him and he just runs with it. So I’m a little stuck on where to go with more age appropriate but also challenging books. I’m thinking some simpler chapter books. He doesn’t like the comic book style as much as a book format and it seems like a lot of the most popular books are written more comic book style. We did Wayside Stories and he enjoyed those a lot. He said Magic Tree House was boring. He was on a goosebumps kick for a bit but decided they’re a little too scary to read alone at night. For non chapter books he likes Dr. suess, creepy carrots series, the smart cookie series.

I’m thinking his reading level is probably around second grade (?). This is just a total guess from googling AR levels from books I know he can read. Looking for any and all suggestions