I camp in South Texas in the summer, and the two things that help the most on hot nights are air circulation and cooling blankets. Look for anything made with Lycocell. You can sleep on top of them and they basically act like heatsinks, or if it's only in the 80's / around 25c and you still want to be covered, there are thin waffle-type ones that are supremely comfortable in that kind of temperature.

Also, if the heat is really killing you, consider a cot: the thin fabric of the cot allows air to circulate under you, cooling off your back as well.