Level depth in various draw functions?

You can use the following overload:
Draw(Texture2D texture, Rectangle destinationRectangle, Rectangle? sourceRectangle, Color color,float rotation, Vector2 origin, SpriteEffects effects, float layerDepth)

To make it function identical to your current code, set the rotation to 0, origin to a zero vector, and SpriteEffects to SpriteEffects.None.