Keep in mind that having upgradable space on any flight is rare, particularly if you book it well in advance. Almost everyone will have to waitlist for an upgradable BF seat. If you're plat and buy a ticket early your chances are very good. If you're silver/gold your chances, especially in this economy, still aren't bad. But as you've discovered it's unlikely you'll be able to confirm the seat at the time of booking. That's just the gamble you have to take each time.