If you’re up to and especially ready to pay for commercial, high-end erotic massage services then there are a few noteworthy studios to pick from in Nice. Paradis (http://paradismassage.eu/) around Promenade des Anglais, behind the Palais de la Méditerranée, has a huge menu of different therapies, such as a 6 hands massage. To me that sounds like a cure for impotence but note it will cost you €450 for an hour.
When it comes to erotic massage, massage érotique or massage naturiste in French, you could also give it a go with an independent masseuse. Some might offer extra services, but usually they will disclose extra options only when you make an appointment. Most masseuses will have a profile on the well-know local or national directory sites and only a few sensual massage service providers will run their own sites. There are a number of masseuses, often of Chinese origin, that offer their services to people on the beach. While their services are far away from an erotic or even a sensual massage, they know what they’re doing and master definitely some skills. So it’s not impossible that with some ladies you could negotiate additional “techniques” in your hotel or private apartment.