Thanks guys. Rang the call centre, he said majority of choice seats and exit rows are still free (he'd quite happily sell me one, but apparently *A silver status lost any kind of perks on US in April) so he said don't worry and when we turn up at the airport to check in (we have an international flight before that) we'd get allocated one of them.

Call centre staff always make me a bit nervous, especially as I perceive it as a popular flight on a popular day, but nothing we can do I guess! They are still selling seats (Seem to be able to buy about 4-5) so that is something... I guess, they can't overbook that much, right!

Thanks for your help guys, maybe I can try and persuade the staff at my starting airport that *A silver gets me exit rows still