Industrial Internet of Things (IIoT) systems require robust mechanisms for secure firmware updates. Existing approaches are often inadequate due to vendor fragmentation, network limitations, and the safety-critical nature of many IIoT applications. In this article, we address these challenges by extending the IETF SUIT (Software Updates for Internet of Things) framework to enhance the security and assurance of firmware updates. Our contributions include the integration of Software Bill of Materials (SBOM) mechanisms and a Behavioral Certification Manifest into the SUIT architecture to increase transparency and provide formal guarantees about the content of the update. The approach is validated by a prototype implementation that demonstrates its feasibility and scalability using real-world benchmarks.