Just a thought, but you may like the bib/coat combination if you try them (refering to the heavy canvas type).
My husband always used to buy one piece insulated coverals. One year needed a pair later in the season... sold out of his size so he had to go with bibs and coat. Now says he wishes he had made the switch years sooner.
He said it is really nice when you get a sunny winter day, to be able to take off the heavy coat and just have your sweatshirt and the bibs on.
Also nice for kids because one can adjust the bibs for length as the boy grows. So he may be able to wear them 2 seasons or more, depending on how much he grows.