This study investigates how Motion Analysis (MA) and Ergonomic Interface Design (EID) can enhance the User Experience (UX) in e-commerce (E-comm) platforms. MA, including Eye-Tracking (ET) and Gesture Recognition (GR), was used to examine User Interfaces (UI) patterns, while EID principles were applied to optimize UI elements such as button size, layout spacing, and navigation. A total of 45 participants, considered by device preference and shopping habits, were observed across PC, mobile, and tablet platforms. Key findings indicate that mobile users engage in more frequent hand and wrist movements and UX higher discomfort levels due to smaller screens and touch-based UI, while PC users reported the highest comfort levels. Scroll depth analysis revealed that mobile users scrolled the deepest, especially during product discovery, while PC users engaged less with deeper content. GA showed heavy UI with more complex gestures, such as pinch-to-zoom and drag-and-drop, while light users relied on more straightforward gestures like tapping and scrolling. EID improvements significantly reduced movement frequency and increased comfort, particularly for mobile and tablet users. The study concludes that optimizing E-comm platforms through MA and EID leads to enhanced usability, reduced physical strain, and greater user satisfaction across devices.