Nothing. Cheapest fully flex would be Y/J - more than B/H. B and H are now useless except for the TPs as all of the cheaper buckets allow changes for a fee, except on day of departure, B&H included. It used to be that the cheapest buckets allowed no changes and B&H did. Now they're all the same. And there are cheaper/nicer ways to get more TPs (e.g., LGW CE trip to AMS or something).