There is a category of product called "mask fitters" which are intended to make your mask more effective by preventing air from escaping around the mask to the sides. As a side effect, your glasses don't fog as much either. Two I know of are "badger seal" (an easy-to-diy design from U-Wisconsin) and "fixthemask" dot com, a silicone strap. I've used the latter, and although it's finicky to put on, it's effective. It's definitely made mask-wearing on chilly days much less annoying for me!