A company runs a reporting platform on an Amazon Aurora PostgreSQL cluster (Standard configuration) that has grown to handle heavy, sustained analytical query loads. The finance team reports that the monthly Aurora bill has become unpredictable and dominated by I/O charges, which now exceed 30% of the total cluster cost. Read query volume is consistently high throughout every billing period. The team wants to reduce and stabilize costs without redesigning the application or changing the database engine. Which action provides the greatest cost improvement?