The correct answer is 'Rightsizing computing resources to match workload demands', because rightsizing involves analyzing the demand for resources and then ensuring that what is provisioned aligns closely with that demand, thus optimizes costs while still meeting performance and capacity requirements. 'Moving to a fully serverless architecture' can be cost-effective but is not always the optimal or possible next step for every workload, making it not universally applicable. 'Deploying multiple instances as a failover in each Availability Zone' increases redundancy and availability, but it also increases costs and is often not used as a cost-saving measure. 'Maintaining high IOPS for all storage volumes', IOPS stands for Input/Output Operations Per Second, means getting higher performance storage and usually increases costs rather than saving money.