Watson, before you do needle up/down at the end of a line of stitching, if you raise your presser foot and move the quilt back a few inches and then bring it back to where it was, that will give you some slack in the bobbin thread which makes it easier to pull it up to the surface using needle up/down. You just want to make sure you get your quilt back in the spot under the needle so the needle goes in where it was last. Hope that makes sense.
Rob