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
This is the last time I'm frogging this project for the last time.