1st...."air markers" are marking pens, usually purple, that disappear after a certain length of time. If you want to speed up getting rid of the marks, just spray with water. They also come with a blue on one end but the blue must be removed with water. It depends on the fabric on how long the marks stay, sometimes they are gone b4 I can sew on them! Other times they last a couple of days. They cost around #3.50 but last a long time.
2nd......If you can't lower your feed dogs, you can buy a 'plate' usually metal that fits over your feed dogs. Then you can free motion quilt on your machine. That works well. I mark my patterns for free motion quilting with the markers (unless it is a stipple or other 'all-over' pattern, then I can try to stay on the lines! I'm not great at it but I'm getting better! Good luck! :?