I have a similar decision to make soon - although there are 5 of us (Me, Mrs L_H, young L_H(11), younger L_H(7)and yet to be born youngest L_H).

I believe your best option is to redeem yours and mrs L_T ona 2-4-1 (100k?)and buy a WT+ and MFU to CW for Little L_T. You then need to add your newborn to the booking after it's born. (I think you'll have to do this by phone or you won't be able to link PNRs or have to book Little L_T as UM.

You should be able to get a good CX package for your BKK flights and hotel - it may be worth checking out if origination elsewhere (eg. TPE) would get you a better CX deal

But, if anyone has any better ideas, I'm open to be corrected.

AFAIK your are correct about BKK - redemptions seem quite rare to be able to find on this route.

Please let me know what you find ~ this could help me.