38-39 is perfect for my wrist as well, for the Breguet case shape. In fact this reference (3657) always sat ideally on my wrist. It even sits better than the 5247 although of same diameter, due to the slimmer profile.
Having experienced so many brands and watches over the years/decades, I can only tell a Breguet tourbillon is made at the highest standards of craftsmanship, up there with anything from anyone - meaning you can’t go wrong imho.
Cheers my friend