It's 777-300ER, at the moment AMS is I think a two class config, versus LHR being a three class config. It's the same J seat.
I've looked at the option of routing via AMS, albeit to KUL, but I imagine BKK to be similar.
All other things remaining equal:
The bad news is the very early start from LHR required to make the 11am ish AMS-CGK flight. This will be a 737, so an economy seat with the middle seat blocked. There should be lounge access in T4.
The good news is you might not need that overnight in CGK either way, as you can probably connect onwards the same day now, gaining you a day in BKK and getting you back to LHR in the morning rather than mid evening.
It was a leisurely faff, but cheap to start with. Now a very very long day both ways.