Yeah, just put a long suit on him or long pants/long sleeves if its quite cold and he should be right.
We have a 2.5 tog for Claire and she used it through winter. We just dressed her in less if it was a warmer night. We would usually just put her in it with just a long sleeved top and no pants on because she would get quite warm and a bit sweaty sometimes. Our house is always quite warm though. But if it was really cold, she'd wear a long suit thing.

Theres actually a guide on their website as to what bub should wear depending on the TOG and the room temperature. I never really followed it though because I thought she'd be too cold in what they suggested, but its there anyway if you're interested.