To fall asleep, your body needs to lower its temperature a little. When the room stays in the mid-twenties all night, that drop never quite happens and you end up tossing and turning. It's not that you're bad at summer: it's physiology.
Did you know? The Spanish met office (AEMET) calls tropical night any night that doesn't drop below 20°C, and torrid night anything from 25°C. If your bedroom is in that range, it's not that you sleep badly: it's that your body has it hard.
What helps most is a shower before bed, but lukewarm, not cold. Icy water closes the blood vessels in the skin and the body responds by generating heat — the rebound is exactly the opposite of what you want. Lukewarm water opens them up and helps you release the heat from inside.
The rest is down to the house: air it out in the small hours and at dawn, then by mid-morning close the windows and lower the blinds. A fan works better cross-ventilating, moving the air around the room, than pointed straight at you all night. Cotton or linen sheets. And thin pyjamas beat sleeping with nothing on, because the fabric soaks up the sweat instead of leaving it stuck to your skin.
Start today: a lukewarm shower before bed and the window open at dawn. Two gestures, zero euros.