Most masks fail at the nose bridge, where the little metal strip has to fight the elastic cord pulling it straight. Here's a 3D printed version I'm ha...ving good luck with. The mask shown fits and works great, but is difficult to sew. It's based on one of the many online downloadable ones, just with the sleeve across the bridge for this to pop into.
Rather than do a fitted mask like this, better to do a pleated version, much simpler to sew
Make sure you leave the ends of the sleeve open, and you can slide it in from the centre, first one side, then push it too far, and then the other side.