I haven't used a straight stitch plate in over 40 years. None of the machines I've owned came with one, and I just didn't think about buying one. But I have seldom had a problem using the zigzag plate for narrow seams. The problem comes from the edge of the fabric being pushed down by the needle at the beginning of the row. I just hold both thread ends firmly for about the first 3 stitches. And I am one who would probably forget to change the plate anyway, as I frequently forget to change the foot!
Happy sewing.