I sympathize with you. I have a Corgi. They look like walking hot dogs. It took me a while to understand this, but my Corgi is a medium size dog just like any other medium size breed. His legs are just shorter. I couldn't find any patterns for him online and had to make up my own. The thing ended up being something like 19 inches long. Good luck trying to get him to wear that thing. My dog hid under the bed when he saw me coming with the completed sweater. I had to coax him out with a dog treat. He never keeps them on.
The next one is a crochet pattern. I know you don't crochet, but this is a very simple concept. You measure your dog's neck, cast on that many stitches, and knit it as one flat piece. It's seamed around the neck when finishing. You can knit an optional tab on the bottom of the sweater and button it on. This was the easiest pattern yet for those long school bus bodies.