Given that our mouths and ears aren't light sensitive, I feel like the best solution would be one that doesn't try to block the light from them.
A standard dark cloth's main two advantages are that they're relatively simple to construct without specific tailoring and fairly easy to carry while still giving you a soft connection to the camera to avoid excessive vibrations or accidental pushing while offering really good light blocking.
But for a bit more design and build effort than a dark cloth we can do the same thing without having to breath into a hot stuffy bag.
The prototypes I was playing with are in a box somewhere, but the two options I was playing with were:
- 'fitted chimney hood': Still trying to come up with a design that folds down nicely, fits around my glasses well enough, and lets me use a mirror in landscape or portrait, but that last bit is probably not important if you don't want to use your camera in a low angle framing.
- Frame and Darkbag: Simple sleeve that goes around the camera and fits to a frame I took off a pair of ski goggles I popped the lenses out of. Sleeve has a little frame to hold the back end open and can quick connect to the goggles with a few magnets. A loupe on a stick I can work from outside the bag makes it easy to use and hard to misplace, while the goggles keep a solid fit that gives me both hands free and works well enough with any hat I wear. [It just looks... very very, lets say 'odd'.]
With either style an open shade cloth over top might still be useful, but since I wouldn't be breathing into a closed or semi closed space while using it, I figure it would be cooler and less of an issue.