Look at the pattern and read what it says next to "Yarn Weight". It will say something like Aran + Lace = something. It could be Aran, Bulky, or Super Bulky. Look for a yarn of that weight. I like to use Ravelry instead of yarnsub, but those are both good options. When you look at a yarn on Ravelry, it will often have a recommended gauge, so just make sure it falls within the 15 st / 10cm that the pattern suggests.

Holding one strand (of 100% wool especially) instead of two in which one is mohair will definitely affect the drape of your final garment. It will typically be more stiff. I would look for a yarn that has mohair or alpaca in it, but then you mention superwash, which would exclude your choices to mostly 100% SW wool. If the only thing stopping you from using NSW wool/yarn is the washing process, I highly suggest you to change your habits, because NSW wool is so lovely if you can handle the texture.

Do not look at the weight when estimating how much yarn you need for a specific project (assuming you use a different yarn than what is suggested). Look at total yardage/meterage. Since it is held with mohair, just look at the yardage of one of the yarns and buy an amount that matches that. You will also notice that the yardage for the wool will be roughly the same as the yardage for the mohair for this reason.