Obviously, as you’ve said, the MS nurse will probably want to discuss the possibility of you starting a disease modifying drug (DMD). It might help to have a look at the various options: https://www.mstrust.org.uk/understanding-ms/ms-symptoms-and-treatments/ms-decisions/decision-aid
However, if you feel that you don’t at this point want to take a DMD, then it’s entirely your decision. The nurse can’t just make the decision for you. Clearly, they all have an element of side effects, so it’s a matter of balancing the positives (ie relapse reduction rate) with the negative (side effects). If you feel that the potential positives aren’t worth the negatives, then just say so. There’s no reason why you can’t change your mine later.
It’s brilliant that you’re keeping yourself so fit. And that wil absolutely pay real dividends, no matter what MS throws at you. Keeping a good core as well as strength and stamina will be possibly the best thing you can do.
So, in your situation, I’d have a look at the various drugs, discuss with your family and/or friends, and make your own decision about DMDs.There are other things you can incorporate into your life, like high dose vitamin D and B12. So you could ask the nurse about these.