Mary, I disagree with you (on paper, because I've not seen you or your students actually roll). I recommend a full pivot - not only a turn of the head, but the spine, and therefore the hips as well. This way the shoulders are entirely turned and cannot impact the ground. This is exactly what happens in a good breakfall, in a sense, lowered to ground level.
Using the method I describe, your body comes into contact with a ground along a diagonal line beginning at the back of the shoulder and going diagonally to the opposite hip. It is NOT a breakfall, and is not intended to be. It is a forward roll. There is absolutely no harm in having the back of the shoulder touch the ground briefly, and certainly it seems less likely to injure than the sort of sideways-across-the-ribs roll that would seem to result by "turn[ing]...the spine, and therefore the hips as well". But I'm sure that I'm misunderstanding what you're describing just as you misunderstood what I described.