Thanks for your responses, guys! And wow, having looked through WearyBizTrvlr's spreadsheet I am shocked at the price differential depending on where one buys the ticket! Strange also that there's little consistency - for example UK seems to be one of the cheapest places for economy, yet most expensive for business. Now I just need to work out how to get to Mauritius!

In terms of my itinery, I've seen a lot of Europe already, so am not worried about having spare legs left over when returning. Your comments about buying it in Sri Lanka then losing the ability to take extra flights in Asia are definitely valid for me.. I'll guess I'll need to have a think about how nice the First experience would be and make a call as to whether I can really "afford" it! I did once fly First with BA out to Mexico City (friend's air miles) and have to say it was a wonderful experience end-to-end. AA back via DFW was no comparison!

In terms of the two DONE3 - I was thinking of flying back to UK from Oz, I presume the "stop" in Bangkok would not count as hitting that continent (sure I saw a post about this a long time ago but can't find it!)..

Either that or I'm now thinking make it an AONE5 starting in Mauritius. Am currently researching how to buy the ticket in Mauritius... I have the BA Travel Shop phone number, but if anyone happens to know whether it can be done through email, that would help!

Thanks! - Sam