“The Chill line is the ideal chunky single-ply (a.k.a. pencil roving) yarn,” says Flynn of Spruce & Linen. This $15 yarn comes in more than 35 colorways and is made of 100 percent merino wool.

The kit comes with everything you need: the exact number of yarn balls your size calls for, an oversized, blunt sewing needle (called, naturally, a yarn needle) for sewing up the sides, a pair of ...