There are many adverts in most Swiss Papers and a great knowledge of the language is not required. Often if you show up at an address it will turn out that the whole block is the on the game.
Quartiergasse (I think this is right). It is North of the River over the Western most bridge.
I knocked fairly at random and the door was answered by a dark haired Argentinean, well into her 30’s and a bit rough about the edges, but womanly and kind and a change from the younger thinner types I normally go for. The price for a BJ and sFS is SFr 100 (GBP 40).