The ease is already in the pattern. I've made hundreds of garments this way and they always fit fine. I learned from a professional, my grandmother. She went to a full-time, two-year professional course to learn. I've taken well over a hundred sewing and quilting classes over the years, and haven't had problems. Sometimes, though, I use a garment ruler that is curved; perhaps you have seen them? I've developed enough skill with this through the years, fortunately, that I often alter patterns or take one part of one pattern and use it with another. For instance, if I don't like the collar on one pattern but like the rest of the pattern, I'll make a new collar piece or borrow and adapt one from a pattern I do like. My grandma could just look at a already-made style and copy it in her own garment without even using a pattern; now that is skill!
Did you know that every size increases the pattern pieces by 5/8 inch? So if you can't get one in your size, you can get another and draw the appropriate chalk lines.
Nancy Zieman has a whole book on the subject, I think.
Last edited by cricket_iscute; 03-03-2013 at 10:03 AM.