My last flat had aircon/central air, but whilst it was nice and cool it made the air horrifically dry and cost a bloody fortune to run, although not as much as the underfloor heating 😱.

My current flat doesn't but there is a ventilation system that draws fresh air in and takes the old out, plus I have a Meaco standing fan which is fantastic and completely silent (OK I'm deaf, but it is very quiet ).

I have a water mist spray for when it's really grim, but tbh I've just been taking the hottest days off. Fortunately most of them have been on weekends so far so it hasn't mattered.

I tried one of those life hack things the other day to cool the room.
So if you have a fan, even if it is only a small one, put it in the open window facing out and turn it on, the theory is that it draws out the hot air in the room and expelled it allowing cooler air in.
If you have a fan that can clip into the window frame then put up high in the window as the warmer air is up high.

My hairdresser tried it the other day while I was having my appointment and it definitely made a difference.