When it comes to your bed linens, natural materials help you regulate your body temperature by wicking away excess moisture and allowing your skin to breathe. Cotton is the default choice for many people - but you could also consider linen or silk. Just think how lovely a linen or silk top feels on a hot day and you'll understand how sleeping under linen or silk can help cool things down for you in bed.
And it goes without saying that the duvet inside your duvet cover has an enormous impact on how warm you feel at night. Again, natural fill duvets will help you and your partner naturally regulate your body temperatures at night - silk, cotton or wool-fill duvets are all excellent choices for someone who overheats at night. Also, consider moving to a lower tog duvet. Perhaps a 4.5 tog duvet is a better choice for someone who regularly overheats at night.
Also, think about your bed itself. Memory-foam mattresses are especially warm at night, so if you have a memory foam mattress to support your body while you sleep, you may want to consider investing in a protector or topper with temperature-regulating properties, such as one made from wool or cotton.