Sound's like things are progressing nicely in dialing it all in. A couple things: for winter trips, I always shovel out all of the snow under my tarp and hammock to get down to bare ground. For me, the ground just seems warmer than having the snow below. 2nd: pillow can help, but it's easy to dislodge, so I use an extra fleece pullover or down puffy wadded up where I need to fill in the gaps.

Do you have a destination locked in your outing this year? There's a couple Michigan winter hangs coming up (Green Timbers hike in with link in my signature) and Ludington State Park car camping, where you can see lots of setups and hang out for the weekend.