Straight line quilting using the seamline, stitching either side of the seam.
No need for marking. Just use your foot as a guide against the seam.
Check your batting as to how far apart your quilting can be.
If the double lines don't give you enough, you could do a 2nd stitch line.
Or go diagonal.
Or if you want it heavily quilted, do continual lines the same width apart, or at random distances.