I transferred to Psychological Science this semester and it was the best decision I made this year. I suggest you take on Biology with communications as the option module, as it's quite useful in semester 2 when you do Psychobiology in PSYC 1B. You can declare your major in your second year by filling out a form and handing it in their office, no need to rush into anything, as you might not even like doing Linguistics once you start studying it (if that was what you meant by complementary course). Overall, it's a chill degree; multiple choice for mid semester and final exams and a few reports to write here and there. If you ever want to get into research/psychologist profession, aim for honours which is offered if you achieve a 75WAM.
Best of luck for the HSC!