ExpertFlyer will show which seats are taken and which seats are blocked for Premium pax and disabled pax.
For BA and a variety of different airlines. For BA, ExpertFlyer looses the seat map about 48 hours prior to the flight when BA locks it down for check-in processing.
It does not show which seats are can purchased by non-BAEC Elite pax (re Upper Deck for example)
F seat selection do not need to be purchased separately.