Dissolve sugar and yeast in 1 cup plus 2 tablespoons warm water in a large bowl; let stand 5 minutes. Weigh or lightly spoon flours into dry measuring cups; level with a knife. Add bread flour, 3 ounces (about ¾ cup) whole-wheat flour, yogurt, oil, and salt to the yeast mixture; beat with a mixer at medium speed until smooth. Turn the dough out onto a floured surface. Knead dough until smooth and elastic (about 10 minutes); add enough of remaining whole-wheat flour, 1 tablespoon at a time, to prevent dough from sticking to hands (dough will feel sticky). Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, for 45 minutes or until doubled in size.