My "summer in the mountains" - which may end up being much like
your winter (I want to be ok down to about -5C in the summertime) is a -3C rated sleeping bag, along with the following - some or more of which I usually sleep in:

1) Fleece Toque
2) 2 merino wool long sleeve T-shirts
3) 1 midweight poly long john bottom
4) a lightweight primaloft pullover jacket (MEC northern lite - no longer made) You could also use something lighter like a patagucci down sweater, or heavier like a fleece.
5) dry warm wool socks.

I also have a poncho like your frogg toggs and a windshirt outerlayer, and I have
pants to wear around camp.

I typically sleep in from just a long john and shirt, up to all of the above, depending on how chilly I expect it to be. I almost always wear the toque at night. I rarely wear the jacket
in bed unless It gets really ugly, or I get sick or something so I'm chilly, although it's
always in bed with me to put on in the morning.

"winter" to me here is a much more serious thing, usually involving the above with the
addition of a full fleece layer, and much more substantial sleeping bag(s)