Sometimes selling sweaters simply isn’t enough. Inside four fashionable boutiques that have branched out into the jewelry business.From New York to Naples Jennifer McCurry is used to her employer’s store, Naples, Fla.–based Marissa Collections, being compared with some of New York City’s swankiest fashion salons. But it wasn’t always this way. Five years ago, owner Marissa Hartington hired McCurry, a graduate gemologist, to help bring her jewelry department up to par with Barney’s, Bergdorf Goodman, and other iconic Manhattan fashion emporiums in an effort to give her jet-setting clientele the one-stop shopping experience to which they’d become accustomed. Jennifer McCurry, fine jewelry buyer for Marissa Collections“We have clients who want us to dress them from head to toe in shoes, handbags, and makeup,” says McCurry, “so why not ­jewelry? We are moving into