You need good measurements for the Perfect Fit? I will have to find a Dutch/Euro supplier as Brexit causes extra import taxes/ extra delivery costs.
When we got Shams' Perfect Fit, we took his measurements, then bought an extra Girth strap in a Medium, just in case we had it wrong or he lost weight. If Hunter is prone to changing size, it's worth paying for an extra piece to adjust for that.
I did find that Perfect fit hugs in the Armpits a bit, but it has Never caused irritation--unlike every other harness I ever used on Shamas.
Alternately, the OP could use a Martingale--I like the Angel martingale. They're leather and chain. Durable, comfortable, and communication with the dog is easy. Shamas got to understand from the slightest movement of the leash. Plus- it's near impossible to slip a properly fitted martingale. Having a reactive dog myself, that's a thing I look for