I am not sure if there is a real difference in soy based and whey based protein powder. There are also organic health food alternatives, based on rice, hemp, and nopales (cactus). Of course they claim that whey protein will kill you 8^).
Since I switched to unflavored protein, I found that soy changes the food taste more than whey or rice. Also, there is a link on thyroid deficiency and soy based products, but I am not sure how serious this is.
Yogurts are great, but plain yogurt (which I like) is eventually getting to be too boring. Fruit flavored yogurts, on the other hand, are full of sugar. I started to buy frozen berries and cherries, and blend some plain (preferably organic) yogurt with frozen fruits and a little bit of Splenda. This creates very good tasting 'smoothie'.
Good luck to you.