I have stayed in both Bolzano and Bressanone in mid-summer. Take seriously the warnings about the heat. You are not in the mountains there; you are down in a valley, and it can bake. The local hoteliers have not yet figured out Climate Change, and many of the moderately priced lodgings are not air conditioned. (The restaurants are mostly not air conditioned, either, which makes meals not so pleasant.) The position of the hotel owners seems to be that it doesn't get terribly hot very often. My position is that I only care about the time when I am there. If it's hot, I want a/c.
Both the cities I mentioned have beautiful historic areas. Bolzano also has the museum housing the Iceman, plus some other worthwhile museums. By all means visit at least Bolzano. But I would definitely stay up in the mountains, at altitude.