Design a comprehensive human-centered system solution for a complex interaction challenge (such as healthcare patient journey, digital banking experience, or smart home automation). Your response should include: 1) Detailed user research methodology with participant selection strategy, 2) User journey maps identifying key touchpoints and pain points, 3) Information architecture design with justification, 4) Interaction models addressing multi-channel considerations, 5) Accessibility strategy going beyond minimum compliance, 6) Measurement framework for user experience success, and 7) Iterative refinement approach incorporating validation methods.