You should be fine with the orps. I think we are similar climate wise. Cold nasty winters and miserably hot muggy summers. Other then a few comb tips here and there out of all my flock with frostbite I have never had any problems with any of them. In the worst days of summer with temps 100 and 80% or worse humidity my flock has learned how to take care of themselves. They either hang out in the barn or wade the creek cooling off and fishing.Buff Orp fact sheet
Cold hardy, not overly heat tolerant, hens around 8lbs.
https://www.thehappychickencoop.com/buff-orpington/