This paper proposes modifications to the Elliptic Curve Digital Signature Algorithm (ECDSA) aimed at resisting emerging quantum attacks while maintaining backward compatibility with existing blockchain protocols. We introduce a hybrid cryptographic scheme that combines classical ECDSA with post-quantum signatures, ensuring that adversaries must break both components to forge a valid signature. Furthermore, we propose a layered security model where each layer independently protects blockchain transactions against classical or quantum threats. Finally, we detail algorithmic adjustments, including larger key sizes and secure nonce generation, to mitigate near-term vulnerabilities. Our evaluation shows that these modifications provide enhanced security with moderate computational and storage overhead, paving a practical pathway for quantum readiness.