The goat breeds from Africa, such as the Nubian or Nigerian dwarf, might seem like the obvious choices, but if someone in your area has been raising one of the Swiss breeds for multiple generations, they are probably pretty well adapted to your climate. I would also stay away from goats with
bucket busting
milk records. Those goats tend to put all of their
energy into producing milk, and they tend to be more affected by stressors such as parasites and extreme temperatures. Cow dairy records say that production starts to go down as temperatures climb above 80 degrees, but in my own herd, I see that the better milkers have a bigger reduction than the average milkers when it gets extremely hot.