Congrats on considering making the move to a new career. Both a formal degree and certifications have their place and have advantages/disadvantages. A degree will give you a solid background in the science behind exericse but doesn’t always give you the nuts and bolts on how to train. If you do a degree you will most likely also need to do a certification as well. That said I have both and I know that my formal education often allows me to understand why I am doing what I do when I train as opposed to some trainers who follow formulas but don’t understand what goes behind it to the same degree. I would echo what Joanne said and if you allready have a bachelors in business consider doing a masters program instead. The university of texas system also has a good program online.
In addition to what Susan and Karin suggested, you should try to attend as many workshops and seminars as you can. There is a lot of new information that comes out continuously, so you must take advantage of it. Usually whatever certification(s) you decide to add to your credentials, they offer many great workshops, seminars and conferences with a lot of information about fitness and nutrition. Most certifications will actually require for you to sign up for a number of such events as part of their continuing education requirements.
Good luck with your search!