I feel I should point out that, while competition in these fields is less fierce, it’s still important to take not of the word “less” and realize that it is still quite fierce. A given tenure-track opening will still likely get well over 100 applicants, and sometimes many times that. One should never bet their entire life and happiness on getting a tenure-track faculty position in any field. Work your tail off to try for it if that’s your goal, but have a solid backup option.
You apparently don’t want to hear this, but I am going to say it anyway. If you don’t even know yet what you wish to study, it is premature to make plans for graduate school. Sure, keep up your grades, get some research experience, and just generally do what you can to avoid losing it as an option, but you shouldn’t be betting your future on it at this point. You don’t even know if you will pass smoothly through your undergraduate studies yet, let alone doing so without a change of heart.