How thick should a mattress topper be?

Across the reviewers we read, 2 inches is generally enough for a minor softness adjustment, while 3-4 inches is recommended to meaningfully revive a firm or sagging mattress. Specialist-community threads on r/Mattress repeatedly note that very thick (4-5 inch) shredded or dual-layer toppers can feel too soft for heavier sleepers or those needing firm support, so match thickness to how much change you actually want.