I would purchase a coat or sweater before you need it. You can buy a size up if you think he will grow much. I have a 9 year old Yorkie that I bought a coat for when I got him right after New Years. He came with a thick sweater so I put that on him to go outside and then bought him a cheap coat at Wal-Mart and ordered him a nice one on Ebay. May we brought home 2 puppies. I just got their coats a couple weeks ago (they match my older Yorkies coat, only they each have their own color) and I bought them the next size up from my older Yorkie as he is my smallest. The puppies are 7 months old and they would have to get pretty big to outgrow these coats. They are slightly big on them now, but not swimming in them. Most coats go by back length so if you measure your dog from base of the neck to the start of the tail that is how long the coat will be and get one that covers them entirely and if they grow a little, it will still cover most of them. That is what I did for the puppies. I had of course tried the older Yorkie's coat on them and although they could wear it, they are longer than he is so it wasn't covering enough of them.
Good luck and check out ebay, there are some really nice dog coats on there. I got one that I love that is made by New York Dog and it is suede and I love it!
I would get something to keep them warm soon in case your temps drop suddenly.
__________________  It's raining Yorkies here! LOL Teek  ,Rowan  , Raksha (Grand Puppy)  , Raelyn |