The manufacturing capabilities of additive manufacturing allow great design freedom for mass customization of different products. This new solution space needs to be explored and served by engineers when designing individual variants of a product. Therefore, the methods of model generation for the individual variant with individual customer specific requirements must be improved to take advantage of this design freedom. This paper discusses the specific challenges of designing a customized car seat by showing its general process chain and the challenges associated with the design of foam replacement structures that offer the possibility to customize the stiffness of the cushion. A possible framework for the underlying digital process chain is then discussed. This framework manages model synthesis according to anthropometric data and safety requirements as conflicting requirements within various complex engineering correlations. In a case study, the chosen Computational Design Synthesis (CDS) framework is applied to the problem of designing an individualized car seat. Detailed descriptions of the concept for each block in the process chain are presented within the case study. The paper and conclusion discuss whether the framework meets the challenges of the application example and further steps for the project.