Massive machine-type communications (mMTC) represent a significant challenge in the fifth generation of wireless networks (5G) and become increasingly critical in the sixth generation (6G) due to the limited frequency spectrum. Addressing the demands of mMTC requires efficient resource sharing among multiple users. Integrating Grant-Free (GF) access with Non-Orthogonal Multiple Access (NOMA) is a promising strategy to improve spectral efficiency. However, it may cause additional interference and complexity at the gNodeB (gNB) side. To mitigate these issues, we propose a novel, low-complexity GF-NOMA framework for joint power and channel allocation, where devices autonomously select their sub-carriers and power levels in a fully distributed manner. Besides, the gNB’s role is limited to sending a global feedback for device coordination. The proposed technique has been validated analytically and through simulation, demonstrating superior performance compared to existing approaches, in particular for the massive access scenario.