I went diving in Phuket 3 weeks ago and had similar total weight as you. I was a star gold so I was no where near my limit. You might also consider business class (about THB2000 more rt) which gives you a biz class seat, 10KG more baggage allowance, access to the Silk departure lounge at both BKK and HKT and a hot meal (vs a cold one in Y) on most of the flights. IMHO well worth the extra expense. TG really packs Y tight, if you get put in 71E find some excuse to miss the flight