Old thread, but I'm curious - OP, what did you decide to do? How has that been working so far?
I'll confess that heating is my chief anti-mustachian weakness, and I keep the house (well, our bedrooms. Luckily we have a thermostat in each room) at 70 at night. The heating bills can get quite high but I made that decision for 2 reasons: a) at 5 y.o. my little one still kicks off the blankets every night, and does seem more prone to head colds when her room at night dips much below 70; and b) even under an epic pile of blankets, I get uncomfortably cold and wake up achey at any temperature below 68.
Needless to say, admitting all that on this forum does make me feel like a complainy-pants, but in my own defense, I never put the AC below 85 or so!
So... long story short, if you haven't already, I would try at the slightly higher temperature and see how your baby does. It might not be that, but it might, and I'd say it's worth finding out. As someone who wears my coat all day in the office, I'm a firm believer that different people do have genuinely different temperature comfort-zones, and your baby's thermostat might just be set differently than yours.