jack russell or jack rat?

Help! My husband and I are confused. We lost a JRT? recently and are devastated. He came from the Humane Society, so we don't know his background. We would like to get another dog like him but don't know what he was. He was 14 pounds, 12" tall, mostly white w/ brown spots, had a huge underbite, and big prick ears. His legs were short and he was stocky. He was extremely affectionate and like to spoon with you while you slept. He looks a lot like other JRT's except for these these things + his head was maybe smaller. Could he have been a "Jack Rat"? Are there regular Jack Russells that could look this absurd? We know we could never replace our sweet boy, but we would like another friend who is similar. We'd appreciate your input!