I was told to look at how I'm dressed then add a layer for bub and when your feeling them to see how warm they are touch thier chest. hth.

Eta- still check thier hands and feet if you think they might be cold. They always seem to be colder than the rest of the body and might need socks on or something.
Ooh and socks... I used socks on DS's hands because they stayed on better than mittens did and they're thicker.