some book options
Here’s a search for light novels, novels, and children’s books in a similar range to rojika (level 22, for comparison) to give you some options!
I’ve personally done 夜カフェ (level 22, also has a wk book club) and the first two magic treehouse books (level 20). I’ve seen people have success with また、同じ夢を見ていた as a first novel but haven’t read it myself yet to vouch. Kiki’s I think people say is actually a bit harder, it’s level 25 but also has a book club. くまクマ熊ベアー is also supposed to be on the easiest end of light novels, if you aren’t immediately turned off by isekai