Okay, so what did I modify? First of all, I did not think that the bonnet needed any interfacing. The ties are too long so I shortened them about 4 inches. I did not use bias tape to make a sleeve for the ribbon, rather I tucked under 1/4" of the last unfinished edges of the bonnet and pressed. Then I edge stitched about an inch in length right on the edge of this turned under bit. This is so that once the ribbon is inserted, no icky raw edges hang out. I then stitched the edge of the bonnet across, leaving the aforementioned 2 small openings for the ribbon. And then made a second line of stitching, 3/4" from the edge to make a housing for the ribbon. This worked really nicely, leaving the bonnet super soft for baby. I had some really lovely striped grosgrain ribbon for the back of the bonnet but you could also make another vintage sheets tie to put in there, maybe a contrasting colour.
I used a bit of solid pink from a vintage sheet border for the ruffle on the bonnet. Cute or what? And it did not take long to make at all!!!!! Now we just need to find a baby for it!