Tenngun, how thick/dense/fluffy is that old blanket you have? The better felted/fulled wool is, the better it will hold together (fulled wool clothing often will have raw edges exposed in the seams since it will stay together on its own). A heavily fulled wool cloth like broadcloth almost becomes felt, and will be near impossible to unravel.
I will say also, that the old blankets shown in the link I posted don't look all that thick and fluffy.... They appear fairly thin, coarse, plain, and not very well fulled... I have some old blankets (not THAT old, but 50+ years old), and while some are not all that thick, they are still fulled up at least a little bit and look better than the British army blanket shown! Of course, I wonder also if it has lost all of its nap over the centuries....