Probably cheaper to fly round trip, test the fit out, and if necessary make any changes at a US Apple Store ?
Unfortunately it was my original plan at first but from my calculations for my own case it is almost the same price than importing it and paying the duties on top of that.
What turned out to be the most expensive is hotel & plane specifically.
It could have been certainly cheaper with some great deals (and if we knew the exact release date earlier!) but only if I don't declare it when going back to my home country which is a risk to take. I would also potentially say good bye to the (big) original packaging (that's kind of a bummer).
And finally the Face ID scan gives me the same result constantly for the light seal so the ordered size should be fine (Hopefully, I cross my fingers). The strap however oscillates between M and S (I ordered M) so I guess we'll see how things turns out and worst case scenario I'll be exchanging one of them.