There are lots of online shops to buy yarns; Blacksheep, Deramores, fabulousyarn, loveknitting etc etc
Just google 'cashmere yarns'
Of course, you have to rely on the pictures for the feel and the colour.
I do knit in a synthetic yarn for DGD1 as she gets a bit of eczema; the others are OK with wool. However, as they get chucked into the washing machine frequently I think something like Sirdar Snuggly is good for children (even older ones) as it is very soft.
One thing I have noticed is that, using pure wool for a garment, be very careful to calculate how much you need if you don't use the yarn specified in the pattern. Because wool is heavier than acrylic or acrylic/nylon mix, you get less yardage in each ball. So check that you buy the correct yardage, not just the correct number of balls.
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