Find a professor at your university that works in a non-math field but is still mathematically sophisticated enough not to bore you. Then take their class (assuming that it focuses on their research rather than being some sort of introductory-level class). Possibly you are unable to figure out if someone satisfies these criteria. If you’re willing to reveal what university you are at, and link to its course catalog, I can throw out suggestions.
You are right in that the real issue is figuring out what field to go into.
The thing about it is that I don’t really know how to taskify “trying a few different fields;” this is perhaps the soul of my question.
Find a professor at your university that works in a non-math field but is still mathematically sophisticated enough not to bore you. Then take their class (assuming that it focuses on their research rather than being some sort of introductory-level class). Possibly you are unable to figure out if someone satisfies these criteria. If you’re willing to reveal what university you are at, and link to its course catalog, I can throw out suggestions.