Hi Kerry,
Try these links:
http://www.wgzimmer.ch (this is mostly for flat share, but there are also some flats you can let on your own)
http://www.immobern.ch http://www.immoscout24.ch/
I recently moved and something you will definitely need is the Betreibungsauszug. This is basically a credit report and all rental companies will ask for it. You get it in Ostermundigen which is just outside (10 mins on the bus) Bern.
I think you'll also need your B-Permit to get this credit report.
I did a short term rental for 3 months, so that I could get settled down and find my way around the city. Then I was able to start searching in my second month. I dont know if this is an option for you.
Any other questions, feel free to ask.