I have a number of BA holiday bookings for the year ahead and only changes I've made so far are to upgrade with Avios with very minimal cost (just the 10,000 avios) and maybe £40 each. I'm finding some amazing deals at the moment through BA holidays buying WT+ and upgrading to CW. You don't even need to pay the additional costs immediately they just take the Avios and then add any extra due to your balance.