Just as one could continue to fly VS, and apply for the Virgin Atlantic credit card which is issued by Bank of America.
BA requires the BAEC account be registered in the same country as a co-branded credit card. This means the same BAEC account cannot be linked to both a UK and USA-issued BA credit card. To my knowledge, Virgin Atlantic has no similar restriction.
I'm suggesting
do both. I'm also assuming that the OP is continuing to bank in the U.S., hence the concern about FX fees on major purchases.
I totally get why you'd stick to Virgin for the TATL traffic. Avios are useless for pure award redemption on that route (short of some sort of inefficient hop through Dublin or Berlin), although upgrading may be a possibility depending on fares purchased. So maybe stick to Virgin there, and the Virgin trains of course. Grab the Virgin CC if it has some nice bonuses. But then use Avios for the short stuff in Europe. That *probably* gets you a deeper pool of flight options than Easyjet.
Of course, where Easyjet has cheap and convenient flights that make even 4,500 Avios a poor value, keep using them. I just think if I lived in Britain, I'd want a stash of Avios to access BA for some short-haul routes where the LCC's leave you at a suboptimal airport or don't operate at all.