I believe it's a control thing and as a parent, you must lovingly show your son who is really in control. The ONLY way I was able to potty train my three children was by removing their pants and letting them go naked from the waist down. You are in a cold region, I totally understand your concern for the temperature, however, I"m sure you keep your home relatively warm so it shouldn't be too cold for your son. Once I had my first daughter potty trained and I decided to allow her to wear underwear during the day, she peed in them. So, I went back to getting her naked and she didn't have issues. Also to note that children get lazy when they have pants on. It is easier for them to pee in their pants while playing than to stop playing for 3 minutes to use the toilet. IF you decide to put underpants on him, I would take him to the toilet ever hour because it's unlikely he will tell you beforehand that he has to go. I never used a special potty chair. I potty trained them right on the toilet because I feel that a child needs to know that the bathroom is in a designated place because what happens when you no longer want him to pee or poop in a potty chair? Then you have to train him to use the toilet. I see that as more work for you, having to clean it out, and then do new training later on. Whatever you do, do NOT go back to diapers because that sends the wrong message to a child. Good luck, potty training is a challenging experience, but oh so rewarding when you don't have to clean dirty diapers anymore.