I put some tips on another post but will add them here in the hopes that they might help someone. If I have to go out, I always take with me a bottle of very cold water that has been in the coldest part of fridge. I leave a washbasin with cold water in it and put hands and wrists in it until very cold. Then I put a clean flannel in it and wring it out just so that it is not dripping, and then put it in a plastic bag. Put it next to your cold water bottle, and you have a cool flannel with you as you go out. When you feel very hot you can then find a shady bit of a path and have a drink and then use the flannel to cool your face , neck and hands. When I am at home I also use the cold water with the flannel to wet my hair and leave to dry., then repeat and you can dowse it in the cold water again and put it round the back of your neck.
If you have old hot water bottle, fill with very cold water and a little ice , then before you go to bed , use it like the old warming pans to cool your pillows and sheets etc. Leave it by your bedside with an extra pillow if you have one. Then if you wake up hot and sweaty you can change pillow - cooler than turning one over and if the cold bottle has been on it it will be worth swapping to try to sleep again. In the day, when sitting down put your bare feet on it. I put a thin towel of some description round it , as it feels better. Modern version is to use those freezer blocks that you put in lunch boxes , wrap with towel and use that. Whilst at home, definitely cotton or silk loose clothes and for ladies , unless it feels too uncomfortable no bra .
If you have to drive somewhere, aircon is good if you have it , but old ways also work. fFew carparks in Britain have any good shade, so my tip is to take with you a bath towel or sheet. When you park then drape the towel over your steering wheel and across to the back of the driving seat. This will help to avoid getting into a too hot seat and wheel. Fold up towel and sit on it to be more comfortable. Cold water bottle and flannel as above but in the side pocket, and if you have passengers can repeat on their side.