A new type of mobility device that functions as both a walker and a scooter is being developed to address some issues of current mobility solutions. Some key design parameters for the scooter mode of this scooter-walker hybrid must be optimized. Through literature, a number of simulated "tests", mostly about safety and manoeuvrability, are developed, and 2100 different possible configurations for the device are generated, with each configuration being rated on the performance for each test using the Analytic Hierarchy Process. Some design parameters tend to affect the test outcomes more, particularly the width of the front of the device and the length. In general, larger dimensions lead to a higher stability, but a lower manoeuvrability. A set of optimized key design parameters is identified, but the methodological framework developed is a useful tool by itself as well.