I have a lot of admiration for you to want to make a lap throw for your Mom.
I would use a warm and natural batting or polyester batting. I would only do straight line stitches to quilt it. I like the stitching about 1/4" from the seam. Stitch in the ditch is where one tries to stitch a straight line in the actual seam ditch. It is almost impossible to do so it looks neat.
Good luck with your throw and I will be happy to see it when it is done.
Welcome to this wonderful board and all the helpful people here.