The advantages of Free/Libre and Open Source Software (FLOSS) in creating accessible, sustainable, and community-oriented technological solutions have captured the attention of the social sector. However, security issues, licensing, training, maintenance, and insufficient use cases require new tools to assist these organizations. This paper identifies which dimensions can be used to develop a FLOSS maturity model for the social sector. Design science research was selected, starting with a systematic literature review on FLOSS maturity models. The study involved four partner organizations from the social sector in Portugal and Angola. Leveraging these findings, we developed a conceptual framework that aligns services usually offered by the social sector with the dimensions that support FLOSS adoption. The evaluation used the system usability scale questionnaire, and the results were further assessed through semi-structured interviews. Our research can contribute to expanding FLOSS adoption in a mission-critical sector struggling to define the best digital transformation strategy.