BA Silver/Oneworld Sapphire here

Travelling JAL in J from BKK to KIX this weekend.

BKK has a range of lounges but which one is best that I can access?
Would I be able to access QR lounge given I am travelling in J, or do I settle for contract/OW lounge? Ideally just to shower/eat and conk out to sleep on the 5hr flight...