You need to shop early if you do not want to be stressed once your body starts putting weight. You can browse online for maternity clothes shops. Try your clothes and see if you are comfortable with the fabric.
Cotton clothes are the best bet as they are light. They give you enough breathing room and you do not sweat that easily. You also need to think long-term. Once the baby is born, you need nursing clothes if you plan on breast-feeding.
Nursing clothes such as shirts and dresses allow you to uncover your breasts for feeding. You can also buy nursing sleepwear that makes it easy for your undress during the feeding time during the nights.
As you put on weight in the second trimester, it is best to start thinking in layers. With the increasing weight and swinging hormones, your body temperature keeps changing. You need to have a wardrobe that can provide you with layers. Therefore, if you feel too hot, your maternity clothes must give you comfort. You can remove the jacket and wear it again if you start feeling cold.