I've used the iron-away stabiliser, it works well, but if it's something you can wash, it's so much easier to use a water soluble. Are you using your embroidery machine for the words, or letters on a sewing machine? If the embroidery machine, then use your heavyweight wss, but try it on a spare bit first, shirting fabric, especially if it's poly-cotton, may pucker so may require two layers.