Definitely both! I run cold. You'll never hear me complain about heat or humidity, but even a little bit of chill renders me somewhat useless. I pretty much always have a down vest and throw it on indoors for an instant temperature boost as needed. I start wearing a sleeveless base-layer when daytime temps are in the 50s/60s Fahrenheit, and once highs are in the 30s/40s, I prefer a long sleeve baselayer. Below freezing, I add long john bottoms.
I've realized I prefer base-layers that don't look too much like undergarments so I can remove layers if need be. The Icebreaker merino tanks are my very favorite for transitional seasons. They are great for boosting the warmth of simple pullovers or button-front shirts, and I don't heistate to wear them on their own. I can't do tight-fitting wool on my arms or legs, so my deep winter baselayers are mostly silk or synthetic if it's really cold and/or I'm going to be doing something active, and cotton or cotton blends the rest of the time.
The past few years I've come to really appreciate thermal long johns under my pants, and I do select pants with layering in mind. A lot of pants are too tight in the leg to accommodate long johns comfortably. I also don't love it when there's a huge discrepancy in rise (like when your pants sit at your hip but your long johns come up to your waist) so I try to pay attention to that too.
Sock layering is my newest discovery. A pair of thin silk liner socks underneath a pair of wool socks does such a good job preventing clammy feet!
