Seattle-based Tom Bihn makes my favorite work backpack, so it makes sense that it also make my favorite mask. They come in several colors and two sizes. To find your size, measure from the bridge of your nose to the point of your chin—my husband and I both wear the small/medium. Once I adjusted the moldable nose strip, it fit me well with no gaps.
We have the polyester-cotton blend masks, which wash well in the sink and are polished-looking and comfortable enough for my husband to wear all day at work. They're made by hand in Seattle, and for every mask you buy, the company donates one to a local charity, which you can track in a public spreadsheet. Tom Bihn is shipping only masks right now, so the delays are considerably less than ordering from other manufacturers.