Erotic massage studios in Frankfurt (full name: Frankfurt am Main) offer the whole package; no need to beat around the bush when prostitution is legal. You can get anything from regular massage and four hands massage to all possible variants of full body massage. But also the rare stuff like getting spanked or golden showers can be on the menu: there are literally no taboos in Frankfurt. Most massage parlors are located around the city center, like Velvet Massagestudio (https://www.velvet-massage.de/) at Bleidenstraße 2 or City Relax (https://www.city-relax.de/) at Töngesgasse 44.
Salons located around the red light district Bahnhofsviertel won’t even bother advertising, they’re open on a walk-in basis and they’re often the best spots around. And if you rather not visit a studio, you can alternatively book one of those independent masseuses advertising on the local escort directories and classifieds sites.