I think I would make a couple of quilts and 'layer' them instead of going for so much bulk in one quilt.
The 'duvet cover' idea seems sort of doable - One could hand baste the two quilts and the wool blanket together while in use and then take it apart to wash the components if/when that became necessary.
I think I would try making something potholder/table protector size first - you'd get something useful out of the sample and find out how well the idea works.