it's usual for tenants to give 3 months notice on an apartment - this should help you figure out when is best to look if 'now' is too soon.
try also
www.xpatxchange.ch I saw a few on there today. Personally homegate.ch as previously mentioned (is also in English) is your best bet.
As in most cities, the closer you are to the centre the smaller & more expensive places tend to be - but's that's a given, right!
If you can get someone who speaks German to go through the contract and be there when you take over an apartment then thats the best way forward.
Happy house hunting.