I understand your point.
My idea was to integrate all these things together with the payment method as part of Itch.io at the developer end and responsibility, but I understand the risks it may involve for you.
Anyway, I would like to recommend this payment processor here:
https://boacompra.com/en
Almost everyone from Brazil uses "Boleto Bancário" as payment method, I could say it's something in a "9 out of 10 ratio" of sorts.
It may be worth for you checking it. ;)
I want to keep selling only on Itch.io from now on, but the majority of my user base is from Brazil.
My sales success depends entirely of this integration.
BTW, keep up the good work! o/
Best wishes,
Alysson L. Neto