Your body needs to drop its core temperature to fall asleep and stay in deep sleep. A warm room or heavy bedding fights that.
Free first: a cooler room (around 16-19°C / 60-67°F), a lighter duvet, a window cracked. Sheets: cotton percale or linen breathe better than polyester or flannel. Mattress: memory foam holds heat; toppers and hybrids with springs sleep cooler. Be wary of expensive "cooling" gimmicks; the fabric matters more than the marketing.
Sleep Picks