Heirlooms are irreplaceable by definition, which changes the math on how much care is worth spending. Documentation and often carrying the piece yourself matter as much as the wrapping technique.
Pro tip: If a piece has significant monetary or sentimental value, consider a specialty antique packing service for that one item even if you DIY the rest of the move.
Watch out: Labeling a box 'antique' or 'valuable' on the outside can make it a target during loading, staging, or a stop along the route.