You have one other potential option which is to book the Euro Traveller price and upgrade later. BA Holidays tends to price upgrades at the cheapest of the difference in price on the day you booked or the difference in price on the day you are requesting the upgrade; and without a change fee either way. The former doesn’t help you. The latter could if the cost of this holiday drops between now and your date of travel, (because for example it was included in any Christmas/New Year sale). Whether that happens or not though is crystal ball gazing.

This policy doesn’t seem to be written down anywhere but it has been my personal experience and that of some other on here, but YMMV.