Tip: if you want to minimize the blueberries or chocolate chips sinking to the bottom while baking, instead of adding them to the batter, you can try dropping a few on top of each muffin after the batter has been portioned into the liners/muffin tin. We tend to not care about those sorts of things, though, and 99% of the time, I make the recipe as written (adding the blueberries or chocolate chips with the dry ingredients).
Yogurt: I haven't tried it, but if you don't have Greek yogurt, you could try subbing regular plain yogurt (just make sure it isn't too watery). I've also subbed vanilla Greek yogurt in a pinch; delicious.