May I suggest something else?
Would the OP's son be willing to wear--drumroll please--long underwear under his jeans? He can get a longsleeved thermal tee to wear under his shirt as well, and get a good fleece jacket/hoodie, mitts and a hat. He'll be warm, and you won't have invested the $$$ for a winter coat.
Remember to thoroughly waterproof his shoes/boots--this will make a lot of difference.
Would the OP's son be willing to wear--drumroll please--long underwear under his jeans? He can get a longsleeved thermal tee to wear under his shirt as well, and get a good fleece jacket/hoodie, mitts and a hat. He'll be warm, and you won't have invested the $$$ for a winter coat.
Remember to thoroughly waterproof his shoes/boots--this will make a lot of difference.