Hi. Welcome to KH. You could substitute any yarn that will work to gauge and that would mean a worsted weight should work. Beyond that, I assume it is quite similar to SS which means that if you don't sub with something similar your shawl will have a different drape. That might be OK. Maybe try a swatch with your chosen yarn and see if you like the way it works up in your pattern. HTH
Happiness is catching that dropped stitch while it's still fixable..