What type of laptop are you going to be carrying and what are the dimensions? What other things will you be taking with you? Power cords? Files? Do you need to carry clothes, etc in this bag as well or just laptop? Do you want to be able to use it for anything else? I think if you provide a little bit more information for us, we can give you some better suggestions.
I'm guessing when you say the Bihn backpack options are too big for you, you are referring the the Brain Bag. It does seem huge to me as well. But if you have a smaller laptop, then maybe you could use the Synapse. Just a thought.