Really excellent reinforcement that! I've used wire before today still in its electrical insulation! Sometimes I make a gemming out of upholstery leather too and add the electrical wire cheaper than a hundred foot spool of gemming! And stronger than canvas!
I’m using a .045 waxed polyester made by the Maine Thread Company here is a link: mainethread.com/collections/twisted-waxed-cord/products/bark-tan-waxed-cord?variant=43448654889200
Short ones are wonderful… there is only one type that are recommended to put into your mouth… they are about 3/8. And in my limited experience, very sharp. I have gone to wire nails, so much cheaper, but not recommended to put into your mouth 👄 due to cancer ♋️ risks.
Your needles are too thick that's why you struggle so much while stitching. It would be so much easier and joyful to stitch with thinner needles. Other than that you doing great job!
These are the thinnest needles available to me that are practical. They are Osborne 2-1/2” 18 gauge. I do have 19 gauge needles. While threading them with thread large enough for the job is “possible” I can get half a welt done with the larger needles by the time I accomplish it. What brand needles do you use?