Where's My Just Right Book?

This is my third year teaching 3rd grade at a low income Brooklyn school, and although by this time I accumulated some books for our classroom library, it is still lacking in certain aspects. Children should be able to choose books that they read independently not only based on their interests, but also based on their abilities. Books have to be matched to readers, but not every child in 3rd grade matches with a third grade book. This year in particular, I have many students in my class who are below the level where they should be at this point in third grade and also many who are above. For these students, it is not always easy to find a book which is just right for them. A book should not be so easy for a child that it lacks a challenge altogether. But at the same time, the book can not be so hard that the child misses out on the story because of stumbling over every other word. Books that are on the right level for each student are what we are lacking in our classroom library. In our school, we use the Fountas and Pinnell leveling system and have a guide listing the levels of hundreds of current and relevant books. This guide is what I am using to put together this "wish list" for my class of books that I know will match the levels and interests of my students. It will be an amazing addition to our classroom library. The students are periodically assessed and always know what their current reading level is. Not all the books the students read are leveled though - I believe that when a student is truly interested in a book, it may be below or even slightly above his/her reading level. But nevertheless, the students have strategies for choosing the books that are just right for them. When they choose a book from our library, the students can open to any page in the middle of the book and start reading that page. For every word that they do not know on that page, they put down one finger on their hand. By the time they finish reading the page, they can tell by the amount of fingers they put down whether the book is just right, too hard, or too easy. 0-1 fingers down means that the book is not challenging enough. 2-3 fingers down, means the book is just right. 4-5 fingers down, means the book is too hard. I would love it if all of my students could find that just right book for themselves! Thank you in advance for helping to build our classroom library!