Luba is right. You can't teach your dog to "go" indoors only sometimes. I would only consider paper training if my dog were very tiny - like 5 lbs.
My pit bull couldn't go out in the cold and snow either, because after literally 5 minutes she would limping and hobbling on three legs - her paws frozen. Of course, having a 70 lb dog "going" in the house is NOT an option, so I had to find a solution.
I just got her some Muttluks to wear. No, she doesn't like them, but she must wear them anyway. Last night I took her out and we walked for nearly an hour. She walked like some prancing pony, but she was so happy not to have her feet freeze!
What I suggest is to get the boots and go to the door and make a big fuss about going for walk. Get your own coat and boots on first, then put his on and go right out. Praise him and even give a treat when he walks in his boots. He'll get used to them if they are connected with positive things like praise, treats, etc.
And make sure his coat is very heavy and warm and covers his bare belly. Old, small shorthaired dogs are SO sensitive to the cold! A friend has an elderly whippet and the dog must wear her coat even in the house!
If your dog is warm - body and feet - he'll like to go out more, just like us.