It is very difficult to adopt traditional materials to our modern ways of practicing woodmanship. It just doesn't make for a good one to one correlation. I'm not aware of any natural material that will be easily portable yet provide good insulation and comfort. Traditionally, ground insulation was accomplished with blankets or furs when traveling by horse, and by gathering vegetation and dealing with the discomfort if traveling on foot. As an example:
"The Bed of a mountaineer is an article neither complex in its nature nor difficult in its adjustment. A single buffalo robe folded double and spread upon the ground, with a rock, or knoll, or some like substitute for a pillow, furnishes the sole base-work upon which the sleeper reclines, and, enveloped in an additional blanket or robe, contentedly enjoys his rest." Rufus Sage, Rocky Mountain Life, or Startling Scenes and Perilous Adventures in the Far West, During an Expedition of Three Years, 1846
"I had for bed purposes, the half of a buffalo robe, an old camlet cloak with a large cape, and a blanket. I spread the robe on the ground, wrapped the blanket about my feet and the cloak around me, throwing the cape loosely over my head to break off the moonshine, and a saddle for my pillow. And oh! I always slept most profoundly. We had tents, but it never raining and but little dew, we did not use them." John Ball, The Autobiography of John Ball - Across the Plains to Oregon, 1832, 1925
As to our bedding, it was not very soft, for we were not allowed to carry more than one pair of 3-pound blankets." Charles Larpenteur, Forty Years a Fur Trader, 1898
"We spread our apischimos on the ground out on the open prairie and covered ourselves with riding cloaks and buffalo robes.... We called to our dogs to lie on top of us, as usual, for the purposes of keeping guard and also of imparting warmth. But those canines were every instant scenting nearby wolves, bounding off with great outcry to fight the beasts or drive them away, then lying down on top of us again, scratching themselves and contesting one another's places. Under such restless, disquieting conditions, especially in our overexcited state, we were unable to sleep at all." Rudolph Freiderich Kurtz, The Journal of Rudolph Friederich Kurz 1846, 1970
The above quotes all involve people traveling by pack train, so they can afford the heavy furs. Kephart and Nessmuk give good descriptions of how sleeping was done with natural materials when traveling on foot. Largely people just slept on the ground wrapped in a blanket.
It was now near dark, and I made haste to make up my flimsy little tent. The ground was desperately rocky. I made out, however, to level down a strip large enough to lie on, and by means of slim alder stems bent over it and tied together soon had a home. While thus busily engaged I was startled by a thundering roar across the lake. Running to the top of the moraine, I discovered that the tremendous noise was only the outcry of a newborn berg about fifty or sixty feet in diameter, rocking and wallowing in the waves it had raised as if enjoying its freedom after its long grinding work as part of the glacier. After this fine last lesson I managed to make a small fire out of wet twigs, got a cup of tea, stripped off my dripping clothing, wrapped myself in a blanket and lay brooding on the gains of the day and plans for the morrow, glad, rich, and almost comfortable. John Muir Travels in Alaska 1879
Since the entire camp outfit and food supply must be carried on these journeys, the outfit taken must of necessity be meager. Only a single blanket and a small, light canvas shelter can be taken and to sleep without a fire under such conditions is out of the question. E.H. Kreps, Woodcraft, 1919
As for my part I shall be obliged soon to make a Virtue of Necessity for I have torn almost all my Cloaths to pieces by going into the Woods; and tho' we do not want for Taylors, We do, Woolen Drapers. Our Excursions, put me in Mind of your going a Steeple Hunting, We sometimes, put a Bit of Salt Beef, or Pork, Bisket, a Bottle of 0 be joyful, in a Snapsack throw it over our Backs, take a Hatchet, a Brace of Pistols, and a Musket, and away we go, scouring the Woods, sometimes East, West, N. S. if Night overtakes us, we light up a rousing Fire, Cut Boughs & make up a Wig-Wam, open our Wallets, and eat as hearty of our Fare as You, of your Dainties, then lie down on a Bed, which tho' not of Roses, yet staying out all Night, accordingly We laid down our Bread an Cheese Wallets, make up a Wig-wam of green Boughs, cut some dry Ferns for a Bed, lit two or three rousing Fires near our Hut, and set down to Dinner. We sung the Evening away, and about 9 OClock retired to Rest, taking it by turns to keep watch, and supply the Fires with Fuel. George Bouchier Worgan in 1788
the night following it thundred and rained very faft, and took us at a difadvantage, for we had made no fhelter to keep off the rain, neither could we fee it till juft over our heads, and it began to fall. One of our Indians cut 4 fticks 5 feet long, and ftuck both ends into the ground, at 2 foot diftance, one from another ; over thefe he fpread his match coat and crept through them, and then fell to finging : in the mean time we were fetting poles nflantwife in the ground, tying others crofs them, over which we' fpread our blanket and crept clofe under it with a fire before us and fell faft afleep. I waked a little after midnight, and found our fire almoft out, fo I got the hatchet and felled a few faplings which I laid on, and made a roufing fire, tho' it rained ftoutly, and laying down once more, I flept found all night. John Bartram, 1744
Anyway, sorry I can't be of more help.