Man I wish I had found this a while ago. But now I can read pretty much whatever I was reading before, but en my target language. It gets so much better at that point. I found it really helped to start with some books you've already read in your native language and then diversify from there. Or in my case I had read half of a really long book series in English then when I went back to it I decided to restart in Spanish. The first half of the series I used my knowledge of the books as a crutch to help with context, then halfway it became new content but I was already familiar with the author's style and vocabulary.

That is a good site idea, thanks for sharing. One of the main time wasting problem I had was finding books at an appropriate level (readability) to read. Their book collection on Languageroadmap is small for french but there are some books there that matches my reading list too, good to see that.

Currently I am doing something similar inside Calibre using a plugin called Count Pages, it support adding readability score to each book and sort them accordingly. It can also display and sort by the number of words in a book.

The readability score is probably not accurate since it is probably designed for english books but I find it mostly accurate so far when I try to read the books to confirm the difficulty. I think some of the scores takes into account sentence length as well so maybe that's why it still works for language like french. Usually easy books use mostly short sentences.