A few of you have asked ... so, the sweater (not coat) that I found to fit our boxers perfectly is the RC Pet Products Cabin Sweater Dog Sweater
Trust me I have tried a few and they all seem to be way to long (because of the broad chest they have) or they are too tight. This one is perfect.
The XL fits both our boxers perfectly (they are 60-65 lbs). Any boxer over 65 lbs, I would recommend the XXL. They have a pretty maroon color too. You can get it on Amazon at http://amzn.to/2D0ZEBr
What sweaters do you love for your boxer?