Even with stuff that stays in the van (or the need for a storage area) I suspect it is still probably easiest to plan to stay in a temporary place for 1-2 months while you get housing sorted. You can try to arrange viewings, but it really isn't guaranteed to be a 2 week process, especially if you want to be in the city of Zurich.

Vision is a well know renter of short term/furnished apartments. Homegate has a category for furnished apartments, though it is primarily known for longer term housing. Beyond that, it is really hard to give advice without knowing your priorities, work neighborhood, etc. Good luck!