I just ordered more transfer paper from Amy tonight. The quality is excellent and the prices are great!
I have used store bought brands in the past and they worked fine, so don't panic if you don't have time to order from Amy. I just think the quality of the ones Amy sells is better than that of the store bought brands.
Also, you don't have to use light transfer paper on light/white shirts. In fact, most of us here use dark transfer paper on all shirts, even light/white shirts. The dark transfers produce a brighter image. The main difference is that the dark transfer paper is white (not clear), so you have to trim around the image in all the spots you don't want the white to show.