Single leaf yellowing?

[Roberta]

Pot can look dry and still be pretty wet. Tracking the weight will give you a more accurate idea of what is going on. You don't want it to stay wet... there needs to be a wet-drier cycle going on. Since the house is on the cool side, you could also consider a heat mat - it will both keep the plant a little warmer, and also dry out the bottom of the pat faster.