You aren’t just heating up your own body w/ homeostasis, you’re heating up the air around you as it radiates off of your body. You will be warmer with tighter fitting clothes. Looser clothes can help with air flow, but if the air is -10°F air flow isn’t your friend.

Insulation is about trapping the air your body has warmed up next to your body, so you don’t need to constantly spend energy heating up cold air.

I’m not sure what sort of activity you’re planning on so I can’t give very good recommendations on exactly what to wear. But I would say just buy clothes that fit you. You probably shouldn’t be wearing so many thick layers that it requires you to go a size up.

Also keep in mind if you’re so warm you start to sweat, once you cool down that sweat is going to make you feel even colder.

Again wear wool, Merino wool if you can. Don’t wear cotton.

Emphasizing what the other poster said, you don’t want to compress anything that traps air. Your best insulator, by far, is trapped air.

Proper mid to outer level layers are made to size so they fit on top of the lower levels