Welcome to the party!
Congrats on your yearling! He might just need more time to start acclimating. Keep him unblanketed during the day, and be sure to brush after you take the blanket off. You might also consider his dietary needs - if he doesn't have any pre-existing sensitivities, you can give him a little extra carbohydrates. Reason being is this: if he's burning all of his energy (glucose and fat) to exist and keep warm, then there's not much left for him to grow a coat. A horse's skin (which includes coat and hooves) is the last organ that the horse's body cares about because it isn't essential to survival. And you've got a growing boy! Where do you suspect all of his energy goes? *wink wink*
So what are you currently feeding, what breed is your yearling, and how much does he currently weigh? Any idea how big you expect this guy to get, height and weight wise?
One thing you can do immediately is make sure that he has forage (grass hay) available 24/7. I can't really make any other recommendations, at least not specifically, until you answer those questions.
No diet, no hoof. No hoof, no horse. No horse is not an option!