I just finally booked my holiday for this November. PIT-JFK-LHR. Back through Philly. So, going on 777 in WT+, didn’t select a seat at time of booking. Will I have issues at Check-in 24/h before? Also I have a bad knee, but don’t require help, prefer aisle seat, hoping one would be open. Would I be denied boarding without paying extra for a seat?

Last time on BA was over 30 years ago.

Thanks in advance.