Making lots of cordage on the fly isn't that easy unless you have ready access to spruce roots which I gather you do. Still, even with spruce roots, I wouldn't want to be gathering much more than needed to build a set of tripods for posts and then lay some boarder poles between them. I'd then simply rest some thumb sized twigs on the frame rather than try to weave it with cordage. Maybe tie every forth one or so to keep it secured. Place pine boughs on top of that. Like Hushnell's picture, simply lash a couple of the frame poles to the tree to save some foraging.
I didn't thought of interweaving smaller branchs instead of tying them to the 2 long pole of the bed frame. The all cordage bedding would probably be more comfortable than wood but at the cost of more cordage.
with cordage only, I would tie 1 end to one of the pole and just run/interweave a 1 piece of 50 something feet of paracord along the 4 side of the bed wood frame. In the morning before keep moving, I would just untie the last knot and roll/unweave the cord back to my pocket. so no cordage lost so i can do the same thing in the new location the following night.
Weaving many small thumb size pole would do the trick as well, and like you said, tying a few of them to keep it in place.. great idea there.