Once, I read from some kind of craft magazine about how to do felted slippers the easy way. No need for soap or hours behind a washbasin. You just need to knit extremely big socks and put them in a washing machine with a big terry towel. Use a normal programme and once taking them out, just pull them on 3-4 number smaller shoes.
The very first slippers I made for myself. Here is a picture of the slipper before putting it into a washing machine. So it is rather a sock.
Here is a picture of the slippers after the washing.