Stephen, "regular" katana length is 180 cm, wakizashi 120 cm. There’s not much of a difference in length needed whether you tie a rōnin-musubi or chō-musubi, even if it appears so in pictures.
220 cm is called chōsun, extra long, and often used by iaidō practitioners.
In order to achieve a nice looking sageo knot silk is best (since it’s rather stiff and holds the loops well), but good quality synthetic sageo can yield a nice result, too; but stay away from cotton, it’s too limp.
Synthetic material sageo are around Yen 1,500, silk usually starts at Yen 4,500.
I would advise against using the cord shown in the picture of your first post, it looks too thin, and doesn’t appear to be proper sageo. Sometimes cords for tying traditional boxes, or obishime for kimono, are marketed as sageo.
In any case, I attached a tutorial on shortening sageo; sorry, Japanese only, but the pictures speak a universal language.
sageo shortening.pdf