Wow! What a beautiful sweater!
My only worry about you switching from the wool yarn to cotton is that cotton is really heavy compared to wool- especially from what I can see about the suggested yarn. I agree with Mirl that you should swatch, but I would encourage you to do a big enough piece that you can see how the fabric will drape.
I have had the painful experience of “converting” a pattern to a new yarn and not being sensitive to the differences of the fibers making up the yarn and how dense the yarns were. While the dimensions were correct, it never hung the way I expected.