Recently, we were experiencing mid 30's and above temperatures and our puppy needed clipping so I booked him into the local groomer. There was a wait time of nearly 2 months. Our daughter did a temp groom (but couldn't get to the knots causing most of the concern), as seen in this pic.
The late summer heat ended abruptly at the time of the booked grooming. The groomer wanted to remove all hair but I suggested she give him a schnauzer trim around the face as no serious knots existed there. He went from a little Chewbacca to a meerkat. Result was single digit temps and a pup with no coat.
We went shopping and the smallest coat was way too big & retailers were caught with the sudden cold snap. I bought the smallest one which is spotty like a leopard. We had one that was too small for our other 4 legged family but he walked straight out of it (green striped one) So my wife suggested a stretchy sleeve. These were good, but he would wet them while toileting.
Days are mostly warmish and he laps up the sunshine.
His own coat is growing.
Prototype done all that was needed was some fine tuning. Another jumper and a pair of kids jeans. We haven't had frosts yet but some nights the spotty coat is placed over the other one he is wearing.
Happy Chappy. Still haven't spotted the right size coat.
Cheers; if you are caught out you too may be able to improvise.