One design change you can make is to take a page from car manufacturers. You get economies of scale when you can use interchangeable components in several models of car. Similarly, you can look at, for example, using identical buttons on many different blouses, or selling the identical model of blue jeans but with different color and trim, so that while you still appear to be offering variety in your clothing, you are actually using a smaller number of components.
Next, you can investigate using less expensive fabrics in your designs. Certain bamboo textiles have the advantage of being eco-friendly and marketable as such to a fashion forward audience, while actually costing less than silk or wool. You also should follow currency fluctuations carefully to see if certain equal quality suppliers have become less or more expensive due to exchange rates.