I did a lot of cold-weather experiments for hammocking, and only got good results when I started using a pad in conjunction with fabric and fiber insulation.

Don't overlook the insulating power of the cheap, closed-cell, foam pad. All the poncho liner insulation compresses beneath you. You'd need a ton of it to keep your bottom side warm. But the pad, while compressing a little, still keeps you warm.

You could use it as an outer, waterproof layer for your bedroll.

Bear