You may well find that there are plenty of seats available when check in opens. I had the same issues on my flight to JFK last week. Two days before the flight almost every decent seat in club was showing as booked so I forked out£65 to get the last remaining window seat (the only other seats left were the doubles in the middle).
Lo and behold, come online check in opening there were loads of seats to choose from, including all those previously showing as booked. To be honest I was a bit miffed but at least I got a decent seat I guess.
So don't worry too much, you may find that not all seats are taken when you come to check in.