Congratulations on a great price! I've wanted a 1947 (my birth year) but got the Cenenneal (sp?) model. Regarding the feet, if you get the short shank feet they will work on the 221. As someone said, the 222 is the same as the 221 but has the removable bed to use the "arm". I would love to have a 222 but they are very expensive.
Graham Forsdyke is located in the UK and he has accessories for sale.
www.singer-featherweight.com That would probably be the closest to you to get further accessories for your machine.