For most people, unless you’re filleting a flat fish (flounder, sole, etc), you’re probably better off using a boning knife than a fillet knife. The flexibility of a fillet knife can be helpful, but it’s also more difficult to control properly. I’d also recommend going in from the back on step 2. With a little bit of practice, it’s quite easy to learn to feel your way around the ribcage, rather than slicing through it and having to remove those bones later on.