Receiving an autism diagnosis in adulthood can be profoundly transformative, yet many newly diagnosed autistic adults experience a lack of accessible, affirming post-diagnostic support. This study explores how a self-guided, neurodiversity-affirming resource--the "Welcome Pack"--supports newly diagnosed autistic adults in navigating their evolving identity. Using a qualitative approach, we recruited 11 autistic adults without intellectual disability in Australia who had received a diagnosis within the past 6 months. Participants engaged with the "Welcome Pack" over a 2-month period before taking part in semi-structured interviews. Reflexive thematic analysis generated four key themes: (1) a sense of belonging through community and representation, as participants found validation in shared narratives; (2) the "Welcome Pack" as one of many tools supporting their self-understanding; (3) emotional reflections, including both relief and grief over years of masking; and (4) challenges in self-advocacy and educating others. While participants described the "Welcome Pack" as an important and validating resource, they also highlighted the need for additional structured peer support and practical guidance. These findings underscore the value of integrating self-guided resources within broader post-diagnostic ecosystems, ensuring that newly diagnosed autistic adults receive timely, accessible, and neurodiversity-affirming support as they navigate their identity.