Southern German here (sitting and sweating in the middle of the night…). I assume our climates are virtually the same.
Admittedly, summers can be really hot and humid here, but there are usually only a few nights per year where it’s really hard to fall asleep because it’s too hot. Nobody has AC, it’s just not worth it for those few occasions. Instead, people cope with more showers, opening all windows and doors constantly, lots of gelato, and hanging out by lakes and pools whenever free. If you really can’t bear it, get a cheap fan and that should save you. You will need a heater for much longer periods of time, and every house has excellent heating built-in.

Also note that the closer your apartment is to the rooftop, the hotter it gets.

Nah. You likely won’t find AC in most places but the thing is most buildings are concrete or brick and nice and cool in the summer, unlike wood homes. Plus you can cool off with Eis-Kaffee