Re the seat size, I would avoid SQ’s 78X with 17.3” seats.
JL’s 789 offers 18.5” width, matched only by SQ’s A380 and B77W.
SQ’s A359 series and Scoot’s B788/789 offers 18.0” width.
JL’s 763 and SQ’s B73M (not offered on SIN-Japan) offers 17.7”’width, which makes it second to SQ’s B78X in terms of narrowness.