First off, instead of making it so that the opening was just along the seam, I made it "envelope" style like a pillow sham. And I did it at the top where dogs and kicking feet spend less time.
|I just went ahead and used the wide seam of the flat sheet for the finished edge on the envelope style closure.|
Then I used a tip I saw on Pinterest: I sewed ties into the corner seams of the new duvet!
|Sewn right into the seam.|
And I sewed a loop onto the corners of the down comforter. I used the seam that I cut off the flat sheet that became the back the duvet for all the ties and loops.
|I used the zigzag stitch to attach them to the existing hem.|
The comforter hasn't crept down or peeked out since! POW!
|All tied up!|