My feet would have been roasting and then sweating in that set up at that temp with say a 35* F quilt–i wonder if perhaps it was too warm at first and your feet started to sweat inducing a lot of evaportive cooling?
Or perhaps you have circulation issues? Â Western Mountaineering Down booties are pretty warm.
With wool socks, basically the thicker they are, the warmer they will be, but the thicker they are, the heavier they will be. It would be interesting if Patagonia or KUIU turned their somewhat unique structured wool into sleeping socks, you’d get a bit more warmth at a bit less weight over the standard ones.
But Apex, Down, etc is going to be much warmer per weight than any wool socks, even specialized, high loft wool.