We’ve used Marmot CWM bags for quite some time now. I know there’s a few others that make a similar bag such as Western Mountaineering.
If you’re moving each night you’ll fight insulation compression. Happens down and synthetic from what I’ve seen. Moisture from your body/clothes pushes into the insulation and never gets warm enough to evaporate beyond the bags outer layer. When the bag is stuffed into a stuff sack, the still moist insulation compresses and freezes. This diminishes the bags insulatory properties substantially. You’ll see folks leave their bags unpacked and strapped to their backs while moving through the day. This helps but isn’t curing the root of the problem.
Using a VBL is really the only guaranteed solution to keep your moisture away from the insulation. Those are not fun, at all. Plan on swapping sleep clothes each day if possible.
As stated above buy the best R Value pad that’ll elevate ALL areas of your body. Anything touching the ground will get cold. For extreme temps consider a thin closed cell pad for below your sleeping pad.
I’d also recommend buying sleeping booties and a sleeping hat. I bought over stuffed models from Enlightened Equipment.