Erotic massage parlours in Naples have been a target of police raids for years already. Many of them are places of abuse for illegal immigrants. Not all sensual massage studios in Napoli are evil, but keep that in mind when looking for one. The tantric stuff like Zen Massage (http://www.zenstonemassage.info/) at Via S. Alfonso Maria de Liguori, is usually a safe bet. Chinese spots like Massaggi Cinesi (https://massaggi-cinesi.business.site/) at Centro Direzionale, often provide more than just massage.
If it would be up to me, I would look something up on one of the Italian escort directories. There is always an escort who has massaggio erotico or at least massaggio classico in her service list. You could also give it a try with Anna from Art of Massage (https://www.artofmassage.it/). Don’t be misled by the name of her site. This mature lady, who qualifies her sensual services as an “exquisite work of art” provides not only tantric and other massages but offers also an intimate GFE, if that would be up your alley.