I've been making hand sewn facemasks for a while. The first ones didn't have nosepieces but I subsequently found a source of them on Amazon.
Mine are rectangular, the size varying for adults and children. the adult ones are, I think, 6inches by 9inches (Imade a template, so have forgotten!). They're 3 layers - cotton, vilene interfacing, cotton - sewn inside out with a gap to turn them through the right way, elastic sewn in place between the layers. Then I turn them through and stitch round the outside again. The family seem to like them and I've sold a few in aid of our church.