In reply to marky:
I have started using an Olympus omd 5 for this kind of thing, small enough to clip onto a harness and also fits in a jkt pocket as a walk around camera and takes great pictures,
Alternatively you can get one of the small Panasonic m4/3 cameras which are even smaller bodies
I use a Panasonic/Leica 15mm lens on it and have really enjoyed the fixed lens.