I use a Billingham bag with my Rollei TLR (2.8 GX Edition). Regrettably, it's an obsolete item called the S3. It's a small bag and it fits the camera perfectly, while providing 2 other small compartments for my light meter and film etc. Looking at the Billingham website the current fStop bags might be the closest, though even the f2.8 is bigger than my S3.

This bag is light and it's easy to load and unload the camera because there are no straps attached to the device. See something worth taking, pop it out, then replace it, easy.

I'm sorry in a way to chip in but I felt that I had to given that I find this camera/bag combination to be one the the best pairings that I have ever encountered. But of course it may just suit me…