Take your machine with you. That's what I did and saved me another long trip. That way u can take it in with u or buy the foot and take it to your car. If it doesn't fit...just run it back in and try again. :)
You definitely want a walking foot. Will almost stop all puckers when quilting (as long as its basted well) and reAlly handy sewing flannel, multiple layers, thick fabric to thin fabric, on and on and on. :). Mine was 15 for my inexpensive singer I used to have and around 25 or 30 for my janome 1600.