You probably can’t go wrong with most of what was read in the Absolute Beginner and Beginner Book Clubs.
Around absolute beginner stage, the difficulty of 三ツ星カラーズ compliments よつばと！ well.
Working my way through レンタルおにいちゃん helped me build my grammar and readiness for things beyond absolute beginner.
Before that, I was reading some beginner-level manga, but was still struggling with it. This includes ふらいんぐうぃっち, 怪盗セイント・テール (which I read with the superpower of knowing it well from the English-subtitled anime and English manga releases), and 俺物語!! (which I was constantly referencing the English release for the first two volumes).