The problem was, I'm always a bit nervous when it comes to cutting good quality leather without knowing, that my pattern actually works.
So I first wrapped my foot in duct tape, cut the mock up open again, placed it on a sheet of paper and traced the pattern to the paper. I then used this pattern to cut my leather (i.e. soles and uppers from different types of leather).
Then you 'only' have to sew the parts together, turn them inside out, and - tadaaaaa! - you have some shoes that should fit perfectly. I was so happy, mine really did! ;)
There are some great tutorials around, I picked out this one (pictures and video):