I frequently see ads of a company called Vision GmbH. They offer apartments with "hotel service" and it seems that they're doing short term rentals as well.

They have a web site at www.visiongmbh.ch, but it doesn't look very useful to me.

You might want to give them a call at +41 1 248 34 34 to find out more.

I've never dealt with them, so I don't know if they're any good though.

andy