Unsuitable non-porous bras often damage the nipples and cause them to lose their natural firmness. During the later months of pregnancy they should be rubbed daily with a few drops of lemon juice to help them regain their proper firmness. Oil or a greasy cream should only be used occasionally; otherwise the surface becomes too flabby.
The breasts themselves also lose their firmness when bras are too tight. A brief daily massage, rubbing from the base to the nipple, will help strengthen them and they should now be allowed to develop freely so that they will not lose shape through breastfeeding.
Then a tip for when you start breast feeding. The nipple is sensitive and the force of a suckling baby is surprisingly strong so start slowly for short periods. The breast is producing only colostrum at this time not milk, so there is no need to latch the baby for long periods to get to the hind milk which is so important later. Latch the baby for 3 minutes and then swap sides and then again and again until the baby is satisfied. This will give both of you a chance to practice latching and will stimulate the breasts which will help with milk production. As the nipple becomes accustomed to the stimulation and suction you can stay latched for a longer time, 5 minutes, 8 and then 10 minutes. By the time the milk comes in on day 3 you and baby are experts at latching and you can manage the suction for a full feed, without the sore cracked nipples!