I was introduced to Perfect fit by my dog trainer and used it for my older dog. In the summer I got a new puppy and wanted to use a supportive harness and immediately wanted to use perfect fit. I emailed them with photos and measurements and they were brilliantly responding asap and advising me the best size to go with. My puppy is now 7 months and I am really pleased. The beauty of perfect fit is that you can change the different parts of the harness as they grow. My puppy decided that he wanted to be huge so had to buy new harnesses BUT I know I'm buying the best harness for my dog.