Your top will peek out under the suit jacket, so choose one that matches the dressiness of the suit. If your suit is conservative, then your top should be conservative as well. Don’t wear a t-shirt under your suit jacket in a professional setting. If you have the opportunity to be creative, choose a top that is a little more edgy. Be sure that your top is clean and fits appropriately. Don’t think that you can just throw on any blouse because it will be under a jacket.
The camisole often has thin adjustable straps and is made of a light fabric like silk, rayon or polyester. Choose a top with a lacy neckline if it is appropriate. The camisole has a lingerie feel to it, so be sure not to choose anything too low-cut, which will be overly sexy.
A shell is a dressy version of a tank top. While the top is sleeveless, the straps are wider than a camisole. The shell can be dressed up or dressed down, depending on the suit. It is very versatile in a neutral color like black, white or beige. You can also choose a shell with a basic, conservative neckline. Or you can try a neckline with an embellishment like lace or embroidery.
A collared button-down shirt will give your suit a menswear edge, mimicking the look of a man in a suit. Some women prefer this conservative look, which can be feminized with a silk scarf or string of pearls. While a white button-down is versatile, a striped or brightly colored button-down goes well with a solid suit.
A turtleneck or mock turtleneck are also conservative options. They are perfect for over-air-conditioned conference rooms and cold winter months. If a long-sleeved turtleneck is too much for you, opt for a sleeveless turtleneck.
A blouse gives a feminine touch to a suit. It provides a secondary outfit if you expect that you will be taking off your jacket. There are many types of blouses and many types of suit jackets. Choose a blouse with a neckline that is complementary to the neckline of your suit jacket. For example, a scoop neck blouse complements a suit jacket with either a v-neck or a military collar.
References and ResourcesForbes: What Women Should -- and Shouldn't -- Wear In the Workplace
Marie Claire: Real Women Try the Trend: Business Chic