Camped a couple of times with woolen blankets, and use woolen blankets at home. The girlfriend knitted a fantastic huge blanket (240 x 200cm), and I was lucky to find a loosely woven soft woolen blanket which was dumped. I prefer these to the military blankets which are very tightly woven and are heavy but not very warm. They are made to last but don't give most comfort. Kephart has a better explanation in his "Woodcraft and camping".
I've used a woolen poncho as clothing and as blanket when sleeping on coal beds down to -7 degrees. Sleeping in woolen clothes (woolen pants, woolen sweater, no warm jackets) and the poncho. I used a german poncho as waterproof barrier underneath me for the rising steam. Slept til the morning without waking up. Mind you another time I did wake up, as I was about to get barbequed.
On canoe trips I've used a reindeer skin underneath and two blankets, sleeping in my clothes. I did not use any fire to heat me, and found it already close to the border at only around 5 degrees in the nights, with no breeze.
I've camped on foot with one blanket and reindeer skin using a parallel fire to heat me. In nights of 0° it was too warm so used the blanket as a pillow. Waking up every few hours to fuel the fire.
What I found from my limited experience is that camping with woolen blankets is perfectly possible all year round if:
-camping in forested areas where (big) fires are allowed
-you have some way of transporting enough blankets to keep you warm (car, canoe, pulka, pack animals)
I really enjoy sleeping next to a parallel fire with a blanket, but it's not allowed in most places..
Sleeping in the tipi we lived in in Sweden we just used two Nanok Endurance -10 zipped together, and extra blankets inside when required. Much more comfortable then just blankets and the nanoks are very durable and cheap as well (in comparison to down sleeping bags).
PS: Why not use a down sleeping bag if you want to use natural materials? Some make their own with cotton instead of synthetic cloth. Using down from extremtextil.de you could end up with a quite light bag, much lighter then a canvas and blanket combo.