I'm going to blog the details for sewing the cover next time, but for now, how to prepare the wool for sewing.
Take an old woollen jumper and throw it in the washing machine with a towel or something else you can wash on a hot wash. Do several jumpers at once to save energy. You need a small amount of wool wash in there too. Do a hot wash with a cold rinse, and you should find the jumpers come out pretty well perfectly felted. You can cut right into that felt and it won't fray.
A good source for old jumpers (apart from your father's wardrobe) is your local op shop. After all, you only need a piece of wool - the fashionableness of the item is not your concern. So you can often pick up a bargain that no one else wants and that would otherwise languish on the shelves (making you feel like a recycling genius). Jumpers with frayed sleeves, moth-eaten holes and stains can likewise be utilised. The only prerequisite for your jumpers is that they have a high percentage of natural wool (100% is not necessary) . That will ensure a good felting. Jumpers with designs and cables are fine too.
Other items you should gather are pants elastic for legs and waist, and polyester thread for the sewing. Cotton thread will absorb the urine and cause leakage. An ordinary needle is fine on the sewing machine - it will be thicker than most fabrics, especially if there were cables on the jumper, but with care you can manage it.
OK - leave your jumper to dry in the shade and take a rest. Next time we'll look at cutting out and sewing.