Hm. I find the opposite of lhrsfo: the coldest flight I've ever been on was LHR-SFO on BA, and it was so cold that tons of people around me were wearing hats and jackets. (I'm almost always chilly, so I don't use myself as a basis for judging.) Conversely, I've been on a lot of AA TATL flights where it's been so warm after the first hour or so that even I am in a short-sleeved polo shirt (and very happy, it has to be said).

My experience has *generally* led me to expect BA to be cooler than AA, and I think this is consistent with the people I've observed - British folks tend to be uncomfortably warm at temperature many Americans (especially those from the warmer states) find pleasant. The very-cold BA flight, the FA opined that the temperature was due to their using fresh, rather than recirculated, air. I don't really see what that has to do with where they set the thermostat, but if that's the significant difference you could ask what they expect to do on the flight you're taking.

A friend with MS and a similar temperature control problem wears an ice vest when the temperature is warm. I don't know how feasible that is for air travel...

wg