Just really overdo the amount of fabric conditioner you use. I half fill the bath and pour about 250ml of conditoner into the water, then when it's well mixed I put in a cloak, about 5metres worth of 60" wide fabric, and leave it to soak for 15 to 20 minutes. Squeeze out excess water and leave it to drain overnight. Then hang up to dry. I do the same for plaids.
I use warm but not hot water, it opens up the wool scales a bit better than the cold.
Woollen pullovers get a similar treatment but I usually just spin them on the wool cycle of the washing machine and hang them on a broad jacket hanger to dry or lay them out flat on an old towel.
I also buy fibre lubricant that is used to stop warp threads fluffling up on a loom, and this works very well to showerproof wool or even cotton. It's not perfect but it does work.
Remember and rinse the bath out really well before you climb in for a shower
Cheers,
Toddy