I hope this is the right place to post this

So I have a work trip that allows me flexibility of airlines - and I even have flexibility of routing, but will need to be into SIN and out of DPS from the UK. But it would be in Y, at their cheapest fare buckets.

I have a big stack of AMEX MR ready to convert to programmes (I normally use AVIOS, but holding back converting for fear of impending devaluation, hopefully unjustified). But BA do not allow WT to WTP upgrades in cheapest fare buckets. I'm looking for Economy to Premium Economy or possibly Business. I'm travelling at a quiet time (november) but appreciate 100% availability for upgrades can not be guaranteed.

So I guess i'm looking at AF/KL, CX, SQ (QF?) for Y to Y+, and chuck in EK & EY & AY (just using SIN/KUL as can easily connect onwards) for a one way Business upgrade - but without scouring every FFP, are their any airline that allows upgrade (at reasonable mileage options) on cheapest Y fare bucket?

Ideas and suggestions welcome! My experience is largely BA Exec club where I normally simply book RFS on a regular basis, but fancy burning some miles with this..