Replying to Camera & Video

Hey NS. So I am getting more into filming and editing, and I was wondering what my next step should be. I use iMovie, and am very familiar with the editing on it. I want a camera that takes great pictures, but I also want a camera that will allow me to take great video as well. I have a GoPro Hero 3 Black right now, and I'm shooting at 2K 30 fps which is great, but if I want to slow something down more when skiing, the 30 fps can get kind of choppy. By using a camera, will this allow me to take better footage, and have a higher frame rate? I guess another question I have is what would be the pros (just focusing on the video part) of upgrading my GoPro to a Canon or Nikon?

I really appreciate your help, and your suggestions for cameras. My mom has a very nice Canon, and I am very familiar with how to use it for photos...just less familiar with videos on these cameras. My budget max would be probably $600.00 but tell me what would be my best option if it is close to that price please.

Thanks!