years ago i used embroider thread, did surgeon's knot. but with my husband sitting on the end of the bed, the ties started coming undone. i took them all out and used yarn. not sure what it was so long ago but it worked. Now not too long ago i used some yarn but after washing it looked terrible to me. i ended up giving that quilt to charity.
crochet thread i will have to look up.

I always use yarn to tie my quilts. Usually it's Red Hart. I have some quilts that are at least 15 yrs old and they are still fine. Using purple will definitely enhance this beautiful quilt.

I've used yarn but love emb floss better. comes in every color.

I prefer embroidery floss or perle cotton (even better)

I watched Donna Jordan's tutorial on tying a quilt. She suggested putting a drop of FrayCheck on top of the knot to help it stay firmly knotted. Thought it was an excellent suggestion.

That tutorial shows making very large stitches and pulling them tight. That is not good. That puts pressure on the fabric where it is pulled together in a bunch. I tie mine on a quilt frame, but I suppose not too many have such a frame. I know it is difficult to get a smaller stitch with a straight needle with the quilt on the table, but you could try to get them smaller. Some use a curved upholstery needle. Then don't pull the thread too tight. The batt needs to be loose and fluffy to keep its insulation quality. When you make the second part of the knot, then pull it tight. Just be sure you have caught the backing in your stitch! ! !

I have always used wool yarn to tie my quilts. They never fall out and get tighter with each washing.

I definitely use a curved needle,large eye. I have Fray Check too. Hmmm.

My preference eto be used with this beautiful quilt would be a Red Heart Acrylic yard but a solid dark purple that is variegated. No matter you are the quilter and what every flavor you like is what it needs to be. Nicely done. Can't wait to see it finished.