Please see newly published advice from the Lullaby Trust:
"We know that the colder months can be difficult for families. You might be worried about paying your heating bills with the increase in energy prices and concerned about trying to keep your home and your baby warm. Whilst we understand it can be tempted to wrap your baby up to keep them warm while they sleep, we know that overheating increases the chances of SIDS and research shows that it's better for babies to be cooler rather than too hot.
To reduce the risk of overheating, avoid using thick bedding and duvets and remove any outdoor clothing and hats when you are indoors. During the winter months, firmly tucked in sheets and blankets (not above shoulder height) or a well-fitted baby sleep bag are fine for babies to sleep in.