Not even a children's book? "La historia de una gaviota y del gato que le enseño a volar" is fun, I read it when I was in my second year of evening school Spanish. I think. Possibly the third. And obviously one doesn't need to understand every word to read a book, I certainly didn't at the time. I still regularly meet words (in English, and much more still in other foreign languages) that I either don't know at all, or only have some very vague notion of. Although if you've never read a book in a foreign language before, it might take a while to get used to the imperfect understanding.