This study investigates the ergonomic needs and comfort levels associated with Non-Driving Related Activities (NDRAs) in Level 3 and Level 4 automated vehicles, focusing on the impact of seating posture, seat adjustment, and pressure distribution. Through a combination of seat adjustment data, skeleton tracking, and pressure analysis, the research identifies the most comfortable postures and evaluates the performance of two different car seats. The findings reveal significant differences in pressure distribution and subjective comfort, particularly in the upper back and neck regions. Users exhibited a preference for more reclined and relaxed postures in Level 4 settings, highlighting the need for enhanced seat adjustability to accommodate individual body dimensions and postural preferences. The study emphasizes the importance of personalized seat features and adjustments to optimize user comfort in autonomous vehicles, providing valuable insights for future seat design in this rapidly evolving automotive landscape.