If you are a native speaker of Spanish I would probably recommend you "Nuova grammatica pratica della lingua italiana" (Susanna Nocchi, Alma Edizioni) - as the title suggests it is grammar-based so it won't help you build all the language skills you need but it will show and teach you the differences between the two languages... and learned those, you are halfway there :)

Hi, look at Alma Edizioni's website.