Typically the best indicator is the back of their neck. Does it feel too warm? Even if their hands or feet may be cold, it’s not as much an indicator of their temperature. My son sleeps in cotton pajamas, no under layer, with a 1-1.5 tog sleepsack and room at 70 degrees. There are some helpful charts if you google “how to dress baby for sleep”. Hope that helps! I know it’s hard to make sure they’re warm enough with the cold weather, but want to prevent overheating too which can be dangerous!
Stick your hand on his chest under the layers does it feel hot? Feet are cold?