I don't know how I ever lived through winters without my Merino leggings. They are warm and comfy. But they were not in a price category I would buy 8 of them.
It's neither necessary nor recommended to wash wool that often. For me it's enough to air them out on my balcony over night and only wash them after several wears, so I'm good with 2. But if that doesnt feel right to you, them maybe wool would not be the best choice for you (or you'll have to replace the leggings more often).