As you've found, there are tricks and techniques for dealing with large pieces of fabric. Grats to you for working through it and learning what worked for you, you'll be able to share that with the next person
I don't think accordion folding the piece so you can keep it on your lap while supporting the unsewn weight was mentioned. Likewise, I've spent many hot months (it always seems like I have a quilt that requires me to finish it in the summer) with fabric slung over my shoulder...