That pattern I actually purchased, I'm not sure who the designer was. I am working on another cat pillow, since I've gotten another cat, and this pattern I did make.

I used Quilt Assistant https://quiltassistant.com/ on Windows to take a photo and turn it into a usable pattern. The software takes a lot of patience as it's an awkward interface IMO. I've tried making a pattern in Photoshop and that was a nightmare.

Once I have a completed pattern I visually QA by printing all the pieces cutting out and laying them out on a big cutting mat. Here's the one I'm working on now. I make sure that there aren't awkward joins or overly boxy corners. It's easy to accidentally delete or move a line while editing, you may not notice that it's not pieceable until it's under the needle. Basically if you notice any concave shapes that pattern probably isn't going to work out for you.