Binding a WPF DataGridComboBoxColumn with MVVM

I've looked at the answers to various questions, but haven't managed to map the content in the answers to the problem I'm attempting to solve. I've reduced it down to the following code (representative of the outcome I'm trying to achieve), and basically want to be able to render the Person.TitleId as its corresponding Title.TitleText when the row isn't being edited, and have the drop-down bound correctly so that it displays the TitleTexts in the drop-down and writes the associated TitleId back to the Person record when its changed.

In short, what do I put in my to achieve this?

App.xaml.cs

protected override void OnStartup(StartupEventArgs e)
{
    base.OnStartup(e);

    var viewModel = new ViewModels.MainWindowViewModel();
    var mainWindow = new MainWindow();
    mainWindow.DataContext = viewModel;
    mainWindow.ShowDialog();
}

MainWindow.xaml

Person.cs

public class Person
{
    public int TitleId { get; set; }
    public string LastName { get; set; }
    public string FirstName { get; set; }
}

Title.cs

public struct Title
{
    public Title(int titleId, string titleText)
        : this()
    {
        TitleId = titleId;
        TitleText = titleText;
    }

    public string TitleText { get; private set; }
    public int TitleId { get; private set; }

    public static List