Libros del Pasaje is my favorite bookstore in Palermo (possibly the entire city). It's so cozy and I always find great books to read or gift here, usually from the employee suggestions set out on the center tables.
For families, there's a huge selection of children's books in the front.
In the back, there's a cafe that is exactly how I imagine Central Perk must have been if it were real. There are cushy, old couches for those who want to chill with a book, and a few tables inside and in the patio for those who want to work or grab a bite.