Are you only flying LGW - BKK? The R fare (GBP 1175) is freely changeable, but probably more than you want to pay.

In my experience EK is unpredictable with inventory because they often block it, so your best bet is reticketing at the very last minute. Sure, around peak periods you'll have a situation where flights really are full and you'll be asked to cough up some stupid fare, but for the most part you'll only pay for one change and get a reasonably good fare.