I took an online class @ Craftsy with Betz White. They're very easy to make and stitch up quick.
You 'felt' old wool sweaters by washing them in hot water & soap. They become dense and don't ravel.
The ribbing on the bottom edge of the sweater is used for the cuff on the slippers.
On the striped pair I used jiffy grip on the soles. I embellished them with scraps left from the sweater.