Use REAL shellac, not any kind of synthetic. 

Shellac is alcohol-based, so when the alcohol evaporates, it's non-toxic.  It dries fast.  It's almost waterproof, certainly moisture-resistant enough for your purpose.  It comes in clear and an amber tint, liquid and spray.

In the U.S., the classic shellac is Zinsser Bulls Eye brand.

Anything that you use it on for the long-term that gets considerable use, be sure to check it once or twice a year to see if it needs another coat, as it will wear in spots.

Warning:  true shellac in its container only stays good for about a year, so buy it fresh in smaller containers, and don't expect it to sit on the shelf and remain good.  It gets thick and sticky, producing a poor finish.

The second one in your list should be perfect.  Remember to give the mask several light coats rather than one or two heavy coats.  I can't emphasize this enough.

If you want to use it on the visible side of your mask, make a quick sample of the paints or other decorations on a piece of scrap materials to make sure it won't cause the paints to run (it shouldn't, but why take the chance?) or give other unwanted effects.

If you click on 'See More Product Details' in your link, even though it says there are no reviews, there ARE ten reviews, giving it a 5-star rating.

Good luck with your project!

Sue

If you don't seal it, it is going to absorb perspiration, get soft, and degrade.

I don't know how the ingredients in regular varnish would affect you if they're absorbed by the skin.

The price shown on that Amazon link is TWICE the price that it is here.  It doesn't have to be that brand, it just needs to be 'true alcohol-based shellac'.  It used to come in small 8 oz cans (liquid).

If you happen to know anyone who does fine woodworking, they may have some lac flakes and denatured alcohol so you could mix your own, but I don't know if you would be saving anything.

I just don't know of any other product that can be worn safely next to the skin.

Sue