Ever since we discovered the Halo Technical Comfort bodysuit, we have not put our son in anything else when he goes to bed.  This is perfect in all types of weather.  We have the short sleeved ones for the summer and the long sleeved ones for colder months.  I like that this keeps my son warm when it's cold and cool when it's warm.  This is also the perfect piece of clothing for when he has a fever because I know that it's breathable.  It's dry-fit for babies!