> I would absolutely be looking into how to get [...] at least one window air-conditioning unit if not a heat pump before next summer
Before you do that, do the cost effective thing: shadow and wind. Then you can add an aircon iff thats not enough.
For shadow, reftrofitting adjustable sunshade is pretty effective. Sunlight brings about 1kw per square meter of window. That like having your heater at full power when its already hot.
For wind: fans, preferably ceiling fans. Lowers perceived temperature by about 3.5 °C.
Uncomfortable heat has nothing to do with temperature and everything to do with air humidity. Only an AC can lower the humidity, by conditioning the air.
> Uncomfortable heat has nothing to do with temperature and everything to do with air humidity
That is not correct. Heat, wind and humidity all contribute.
In a dry air with no wind, your body creates a "hot and humid" bubble around it if you are not moving. A fan helps.
Humid but neither cold nor hot air may not feel great, but not that bad.
Hot and humid air with no wind, now that's bad.
Edit: I know because I added shades and fans.
27 centigrade with 80% humidity is a lot more uncomfortable for the human body than 33 degrees with 40% humidity. Likewise if the temperature is low, it's worse with high humidity and vice versa. The worst heat is the humid heat, and shade and fans cannot do much about it.
Shades will bring your 27C to 24C so yeah, it would do much about it. I don't even get your logic here.
Edit: you can still use an AC or dehumidifier on top of it. You will consume less energy with shades.
Letting the sun in is like letting your heaters on. You would not turn on both heaters and aircon in summer, would you?