Cool the bedroom

A hot bedroom means less deep sleep and more waking. That comes from a review of how heat and cold affect the sleeping body. Evidence: decent Cold under warm covers doesn't break up sleep the same way, but it still affects the heart. Cool, not cold. Evidence: decent

There's no single best temperature. You'll see exact numbers online; the research doesn't give one. A practical test: cool enough that you want the covers. Evidence: worth trying

If you have a heart condition, don't sleep in a cold room in winter. The same review ties cold nights to strain on the heart. Evidence: decent