Unity Static Singleton JSON Serialisation

I have a static PlayerData singleton which stores all the data for the player (gold, upgrades, heroes etc) but JsonUtility cannot serialise static or private methods so I have implemented a singleton with an intermediate SaveFile struct which is used in the serialisation.

PlayerData will have more complex objects likes HeroCollection etc but for now, I simply have a gold stat.

I am looking for a potentially better alternative solution or simply how to improve this.

Thanks.

struct SaveFile
{
    public int Gold;
}

public class PlayerData
{
    static PlayerData Instance = null;

    // # - Private Attributes - #
    int _Gold;

    // ... Heroes
    // ... Upgrades
    // ... Etc
    // # - - - - - - - #



    // # - Public Static Attributes - #
    public static int Gold { get { return Instance._Gold; } set { Instance._Gold = value; } }
    // # - - - - - - - #

    public static void Create(string json)
    {
        if (Instance == null)
            Instance = FromJson(json);
    }

    public static string ToJson()
    {
        return JsonUtility.ToJson(

            new SaveFile()
            {
                Gold = Instance._Gold
            }

        );
    }

    static PlayerData FromJson(string json)
    {
        SaveFile save = JsonUtility.FromJson<SaveFile>(json);

        return new PlayerData()
        {
            _Gold = save.Gold
        };
    }
}