If you used the BA prem amex rather than the Amex rewards card you'd generate 50% more avios (1.5 vs 1 per £). Also if you're short of a few you can buy a top up which probably works out cheaper than paying cash for the flight. I get a lot of my avios through using topcashback and gate365 and have just booked our second F trip. With slight changes to your shopping habits is amazing how many avios you can get.