I hand quilted a quilt already and I only used a single thread, using the same thread you are. I don't think you'd need to double up as it's a thicker thread. And I think I might go through with it as I'd only need to make 3 blocks, and I'm in the same boat as you, but I think my machine broke (yikes!) and as it's a Bernina, I think it'll be expensive to fix. Good luck and I know it'll look pretty when you're done!