There is a book called The Eyelash Geckos, Care, Breeding and Natural History by Andreas Kirschner, Hermann Seufer, and Yuri Kaverkin. I found this book to be the best source of info on Goniurosaurus, although it does cover more than just that genus. It includes pictures and descriptions of quite a few the species. Also, I believe that the book is originally published in German, although my copy is in English, which may be helpful to you as I noticed you appear to be located in Switzerland and that might make getting a copy easier.