As this all drags on, it occurs to me that other singers might benefit from what I have been doing.

I have homemade masks that are basically cheap baby bibs, with terrycloth backing, which I extend around the back of my neck by attaching fasteners. (I got better results by attaching black hair scrunchies on each side of the bib and then tying the two scrunched together at the back of my neck, but it is possible to use straps or shoelaces or ribbons.) Bibs today have Velcro to close them, which might be used for a neck strap extender; but since I use the sewed on scrunchies, I cut through the stitches holding the Velcro to the bibs and just throw the Velcro away.

The primary advantage is that baby bibs are extremely washable and are made to be bleached, and thus are sanitary. The terrycloth backing is soft, and wicks moisture or humidity away from the face. Using a neck extender tie instead of ear loops allows a better seal around the nose (no condensation fogging glasses), and the hang of the fabric allows one to breathe and sing without sucking the mask against one's face. There is also no way that droplets (if they exist) are getting through a baby bib, and it totally blocks sneezes. I wear these at work, which is a physical job, and seem to do better than a lot of my colleagues. They are not too hot or too cold.

The packs of four baby bibs that I use are very cheap and were bought at dollar stores; the packs of hair scrunchies that I use are actually the more expensive piece. I happened to have beading wire and no good needle for the purpose back when I started, so I actually sewed on the scrunchies with short pieces of wire then, and this "sewing" has gone through the wash okay for most of the year. (But actual sewing is better.) I have twelve masks like this, and they are very sturdy.

The disadvantage is that it looks a little silly. The design also might be too small for men, although I have a big face and head for a woman. And yeah, there is still a carbon dioxide buildup problem, even though the mask is open along the bottom edge. Early in the day, this is not a problem; it is the moisture buildup that does it, after eight hours or so.

Hope this helps.