When decided on a sleep sack for the winter, there's four things I've always looked out for. Firstly, the material. I've always gone for sleep sacks made with natural, breathable fabrics like cotton or Merino wool. These materials help regulate your baby's body temperature by allowing airflow and reducing the risk of overheating. Wool is particularly good in winter as it's naturally insulating and moisture-wicking, which keeps your baby warm without making them sweat. I tend to avoid synthetic fabrics, as my daughter sweated all night in one once, even at the height of winter. Next, check the TOG rating. For winter, I go for a 2 to 3 TOG, but it does depend on how cold your house gets. A 2 TOG sleep sack would be best if your child's room is between is 16degC and 20degC at night. For colder rooms, you might want to go higher. You can always add or remove layers underneath the sleep sack when temperatures fluctuate night-by-night e.g. by adding a long-sleeve vest or onesie. It sounds obvious, but it's vital that your baby's sleep sack is the right size. The sleep sack needs to be well-fitted around the neck and arms, ensuring that it can't slip up over your baby's face during the night, especially when they become more mobile and roll around more whilst asleep. It should also allow enough room down below for your baby to move their legs freely. The final choice you'll have to make is to go sleeved or sleeveless. Most sleep sacks are sleeveless, which allow for better air circulation and stops baby from overheating. However, if your house gets especially cold during the winter (14degC or lower) you might want to consider a sleep sack with removable sleeves, or at the least dressing baby in long sleeves underneath. Even if especially cold though, avoid adding blankets or anything loose or heavy that baby could wriggle underneath in the night. More clothes are more effective and safer. It's recommended that your baby's sleep space should ideally be between 20degC to 22degC all year round-but obviously that can be tricker in winter. To check if your baby is too warm or too cold, feel their chest or back-not their hands or feet, as these are often naturally cooler. Use this as a reference to know whether you should be adding or removing layers.