Silicone Mask Adjusters
I have found with my masks the two sizes of mask I offer, seem to work for everyone, however I do offer these silicone elastic mask adjusters. They work best with 1/4 elastic straps like the masks I make.
There are a few videos out there showing how to put these one. A crochet hook works best, but you can use a bobby pin or needle and thread. Checkout YouTube for great how-to-videos.
The cost is 50 cents for a set (one for each side of a mask).