When it comes to moving your quilt in free motion it really has more to do with the free motion foot you're using. If the foot is resting too low and squishing your quilt, it's going to be very noticeable when you leave the feed dogs up.
You want your darning foot to just skim the surface of the quilt. You can then leave your feed dogs up, turn your stitch length to 0 and start quilting.
If you really want to cover them, a supreme slider really is excellent for making the quilt easier to move. An alternative would be an index card with a hole cut out in the middle for your needle - just make sure to tape it down!
Experiment a bit with a small 10" square with the feed dogs up, then down, and see for yourself what works the best for you and your machine.