To ensure the right fit when purchasing a short night dress online, it's essential to consult the size chart provided by the website. Measure yourself accurately and compare your measurements to the size guide to determine the appropriate size. Additionally, consider the desired fit – whether you prefer a loose and flowy style or a more fitted silhouette. Some nightdresses may have adjustable straps or elasticized waistbands that allow for a customizable fit. If you're unsure between two sizes, it's generally recommended to opt for the larger size for a more comfortable and relaxed feel.