Or a straight stitch presser plate instead of the zig-zag plate.

You might try lightening up on the pressure of the presser foot. There is usually a screw on the top of the machine that controls this. Remember, righty tighty, lefty loosy. This is especially true if you are not able to drop the feed dogs, like on the older machines. In that case, be sure your stitch length is set to zero; this will help keep those feed dogs in check. Feed dogs moving forward will make it harder to sew backwards, even if you are using a free motion foot. With light enough pressure, you should be able to move the fabric freely under the foot (try it without moving the needle). If you cannot move the fabric easily with the foot lowered and you are not stitching, then the pressure is too heavy on your foot.