I have some Mamiya TLRs, and when I want to go minimal--I use a medium-sized Zing neoprene pouch. It easily slides over the camera, only weighs a few ounces, and works well to cushion the camera with minimal extra bulk. This assumes you have a strap attached to the TLR.

http://www.bhphotovideo.com/c/produc...ing_Pouch.html

If the Zing isn't readily available, I'm sure you can find something similar.