The buds take a while and might be firmer still because they're closer to the muscle itself, later on when they are larger and round out more, boobs feel more like when you press a bit in the butt (albeit slightly jigglier and more sensitive like your lips).

Soreness is normal in growing boobs, esp when pressing (or when you're breastfeeding).

Other than that I don't know - as another has said, touch your boobs every now and then to feel.