Definitely the IDEA website and your own since you already have one. Not sure if you need more than that.
Word of mouth is the best, so it’s wonderful that your business is growing that way. Also, since you have happy clients, it’s also a great way to build your testimonial section.
Good luck to you!
I saw that you have your own website. The thing is for people to find it when they are looking for a personal trainer in Charlotte, NC. While I am not an expert on Search Engine Optimization, I know that the more you are connected to other sites through links, the better your chance of showing up in some of the first spots if people google. And once you link people to your site, they may return the favor.