As for the choice of major, it depends on what major you like. I suggest that you can take courses in those majors now and choose a major you like as your goal. Then, you are only a sophomore, so you can lay a good foundation, especially English. Because you are a math major, math should not be a problem. The key is English, especially to learn English well. It will be much easier to review in the future.
For the choice of school, you can choose your favorite institution, but you should also refer to the admission scores and the number of students in previous years, because many schools will occupy a lot of places if their undergraduates leave more, so few people will really pass the exam, so the competition will be fierce, so I suggest that you must find out the enrollment or choose a school with a large number of students.
If you can, you can also listen to free lectures organized by many postgraduate institutions and collect postgraduate information ~