I´m not sure where to read easy manga for free but try this:
https://learnnatively.com/search/jpn/books/?tags=free
Also on bookwalker, you can often read the first X volumes of mangas free for a period. Right now we have a speed club for this: 花野井くんと恋の病 Vol. 1 | Free to read through Nov 9 (JST)
This manga is in the lower rating on natively and you can always ask questions about grammar structures etc!