Well, I finished quilting it! Thanks to all those offering suggestions and moral support, they were very much appreciated!!!
A weird thing: I had another quick go (prior to the larger needles arriving), and had no problems! Somewhat amazed, I went through two whole spools of bobbin thread with no breakages, before I suddenly realised I'd raised the feed dogs to do a quick fix on my daughter's clothing before she went out: I had changed the machine feet but forgotten to drop the dogs again. So I dropped them, and two thread breakages in less than five minutes! I raised the feed dogs, and managed the rest of the quilt top with very few problems. I know some have suggested keeping the dogs raised for FMQ, but I am amazed it made so much difference to me - I still can't work it out
Of course I have run out of thread half way around the binding now, lol!
The larger needles have just arrived too...