I just picked up a MissionWorkshop Rambler and it seems perfect for your needs. The way it opens up to swallow anything but is compact the rest of the time is pure genius. I've had it for four days and keep commenting to myself how incredible it is. It has replaced all of my Chrome two strap bags. It is way more comfortable and practical on and off the bike. It's made by the orignal founders of Chrome (they sold Chrome two years ago) and is the bag they have been wanting to make for a while.

I know you want to try local, but given your requirements and your goal to get a back that will not need to be replaced soon, check this one out -- you can always order it and return it if you don't like it. Here's the link: http://www.missionworkshop.com/.