Well, while I was writing my lengthy instructions I see that you do not want patches. Here's another way.
Use a large sheet of clear plastic--we use the kind you get at Home Depot or such .--they are sold as drop cloths.
Lay your sweat shirt out and lay plastic on top. Smooth and pin down and trace sides and seam lines with a sharpie.. This will be your pattern. Add seam allowances to what you have drawn on plastic. Cut it out.
It really works. I've done it twice also.