It's not all in the sewing. If you are losing an 1/8" each seam, it's probably also due to cutting, pressing, and thread. I've struggled with this myself and using 50wt thread (Aurifil or Masterpiece for me, but Mettler, CT, and others also have 50wt), pressing carefully with a hot, dry iron, and cutting just a few layers at time, carefully, has helped as much as careful sewing. My favorite piecing machines are my Berninas, in part because of how great the 1/4" feet (one with a sturdy right guide, one without). Featherweights are also great for piecing and there are so many aftermarket feet for them that you are sure to find one that suits you. My Quest Plus is also a great piecing machine. Another big help is a screw down seam guide.