Never heard of double stitching before except to adjust a seam, but I always backstitch the beginning and end of every seam. I made a queen size Rail Fence quilt one year and did the assembly line sew and cut into segments. Oh, what a mess. By the time I went to sew the blocks together, every seam was becoming undone so I restitched EVERY one. What a chore. Also, my friends sister made her twin grandchildren quilts with quality material, short stitches, and because the twins were always tugging the quilts, the seams were always coming undone. In checking, the sister didn't backstitch any seams, just thought the sewing at the intersecting seams was all that was necessary. Those kinds of repairs, close to the seams , aren't fun to repair. My backstitching has never caused thickness and will continue to do so. I'd rather take the time to backstitch than to repair later. That's my story and I'm sticking to it. lol