[CustomPropertyDrawer(typeof(TestSprite))]
public class TestSpriteDrawer : PropertyDrawer
{
    public override float GetPropertyHeight(SerializedProperty property, GUIContent label)
    {
        float baseHeight = EditorGUI.GetPropertyHeight(property, label, true);
        return baseHeight + 130f;
    }

    public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
    {
        Rect spriteRect = new Rect(position.x, position.y, 128, 128);

        SerializedProperty spriteProp = property.FindPropertyRelative("mySpriteTest");
        EditorGUI.PropertyField(spriteRect, spriteProp, GUIContent.none);

        Rect restRect = new Rect(position.x, position.y + 130, position.width, position.height - 130);
        EditorGUI.PropertyField(restRect, property, label, true);
    }
}