Are you in the South, OP?
You can strip your bed and cover it with some cotton sheets. It is important they are actually cotton and not anything else. If you have grandparents who is still living, it is a good chance they have real cotton sheets...the ones that have a bit of weight to them but that are also cool. Ask them for some. I'm not sure where the older folks get these sheets from...I only say ask because I still have never successfully found anything close to the quality of bed linen I used to sleep on at my granny's house as a kid.
I should say, the cool cotton sheets are integral to the entire plan. I don't see it working any other way.
Once that is out of the way, you will need a little cooler. Fill it with ice and stock it with fruit, prepackaged salad and sandwiches. Put some bottles of water and Gatorade in there as well. No milk and no alcohol should be included in your beverage selection. Keep the cooler next to the bed.
Next, go take a nice hot shower where you use soap and a washcloth to get off the yuck off your bed and hit all the cracks and crevices until you are squeaky clean all over. Then change the water to cool before you get out and stand in it for about a minute. When everything on your body has tightened up from the cold, it's time to get out.
When you get out, dry off slowly (you can stand in the corner and drip dry on a towel) and just lay nude on the sheet-covered mattress. Make sure your body is completely dry before you lay down.
Make sure your blinds are closed as to not let in sunlight. I wouldn't open the windows much if you don't have good screens (i.e. screens with no holes) covering them from outside. If not, you are just asking for flies and mosquitos to invade your space and cause major problems.
Now, just enjoy your space! Enjoy the coolness of the bed. If you are dealing with major heat, then remember, it's too hot to move and it's too hot to cook and eat.
Movement generates heat. Cooking obviously generates heat. Eating generates heat, too, when your body starts digesting the food.
So, if you really feel you must eat, reach slowly and grab yourself one of those pieces of fruit or salads or sandwiches from the cooler next to your bed. You shouldn't have to reach too far.
Chew slowly, sip slowly, swallow slowly - anything to reduce movement external and internal movement.
Just be still as much as you possibly can for as long as you possibly can.
You'll have to go to the bathroom at some point. If you go to per, come back and get on the opposite side of the bed where the sheets should still be 100% cool because they weren't warmed from your body heat. If you have to poop, this may give your entire bed time cool back off because you will likely need to shower again to make sure you don't bring back errant shyt and accidentally streak your bed when lying back down.
** If you skip the eating altogether, though, you can reduce the need to go through any of this.
Also, because so many of our electronic devices produce heat, stick with using a phone or tablet versus laptop on the bed. Those things get very hot and, thus, you'll be hot all over again.
Lastly, it should go without saying, sex of any kind is a no-no because it produces heat, and then a mess you have to clean up...which, in turn, just means you are moving more and getting hotter. Plus, it is going to mess up these sheets which may have been hard to find in the first place.
Remember, abstinence is the name of the game if you want to stay cool - no eating unless necessary, no talking aloud, no sexing, no crying, no hard breathing, no hard typing, no hard swiping....no unnecessary moving of any kind in the dark on your cool sheets.
You can do it. Hope this helps, OP.