Turtlenecks come in a variety of cuts. The classic, tight-fitting turtleneck sweater can be combined in many ways: Tuck the sweater under a skirt that you wear at waist level, or into pants. That way, you visually create a slim torso.
Make sure that you wear a bra with slim edges that do not stand out too much when wearing a turtleneck sweater that is made of a thinner fabric.
In other words: In this case, it's better to avoid lace bras and go for a plain bra. Turtlenecks are also available in oversize style, long versions or with a zipper. These are best balanced with a tighter skirt or pants, so that the whole outfit looks neat.