Though my button stash is limited (I don't stash buttons, most of what I have are taken from garments that were at the end of their life cycle) I still have four options. The good think about them is that they are all the same size.
The picture doesn't show the fabric too well, it has black, brown and dark blue in it.
Burda magazine did use a smaller button. I measured with one of my buttons and the green line in the second picture defines the new buttonhole length. The red marks are the original pattern marks.
Another thing to check when using a larger button is to make sure the button will not go over the edge when finished. That was ok with my buttons.
The pleat in the front is sewn and folded down. Burda gives no instruction how to handle the bulk that as a consequence is in the waist seam line. the inner part of the pleat is in the way of the buttonhole.
My solution was to cut away part of the fold and zigzag the edge. After sewing the waistline seam I held it in place by a catch stitch. Not the most beautiful hand stitching, but it works and will never be seen.
After this I sewed the shoulder and side seams and could put it on to see the fit. I think it's promising to be good. Too dark to take photos, especially as the fabric is rather dark.