> 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.