Alpaca is good, but it doesn’t retain its shape in the same way Wool does, which makes it much more prone to stretch. Thus, I wouldn’t use 100% Alpaca for something that needs shape (hats, sweaters, etc.).

I find linen difficult to work with. You might try bamboo, and some silk blends. There is also seacell: http://www.knitty-noddy.com/component/page,shop.yarn_flypage/product_id,1616/option,com_phpshop/ and of course microfibre. Cashmere is awesome, but expensive. There are cashmere blends that are less expensive. Merino wool tends to be the softest, and so might not bother you too badly.
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