Using C# code in SharePoint WebPart

Question

I have used the below C# code in SharePoint 2010 webpart to get hold of my configuration settings,

string _configInfo;
[Personalizable(PersonalizationScope.Shared), WebBrowsable(false)]
public string ConfigInfo
{
    get
    {
        return this._configInfo;
    }
    set
    {
        this._configInfo = value;
    }
}

private HiddenField sourceListConfig;
protected override void CreateChildControls()
{
    this.sourceListConfig = new HiddenField();
    sourceListConfig.ID = "SourceListConfigID";
    sourceListConfig.Value = this.ConfigInfo;
    this.sourceListConfig.ValueChanged += new EventHandler(sourceListConfig_ValueChanged);
    this.Controls.Add(sourceListConfig);

    base.CreateChildControls();
}

void sourceListConfig_ValueChanged(object sender, EventArgs e)
{
    this.ConfigInfo = this.sourceListConfig.Value;
    this.SetPersonalizationDirty();
}

Server side coding is restricted on latest versions of SharePoint. So, how do i implement this for my webpart in latest versions of SharePoint like 2013/2016.

There is a "Properties" in webpart's "Elements.xml" that we can use in webpart configurations. But, i have a lot of controls to get hold of it's value. So, i can't use that. Instead i have used a long string that holds the value of webpart controls. For example, i have 10 checkboxes and i will hold those values in that string and also update when it gets changed. I just used the checkboxes just for understanding and also i am using more than 50 controls in my webpart.

What is the recommended option in latest versions of SharePoint?