Your initial code is correct, but instead of creating child classes of the Data Asset class, you need to add it like above.
Think this is more correct answer to it.
However I still reference them as soft object (just checking from my inventory system)
UPROPERTY(EditAnywhere, Blueprintable, BlueprintReadWrite, Replicated, Category="MGInventory Component - Variables")
TArray<TSoftObjectPtr<UMGInventoryItemAsset>> InventoryData;