Elizabeth, I've always found my thin merino cami with a cashmere topper is so breathable that it's never clammy. It keeps me warm when it's cold, and breaths when I'm warm, if that makes sense. I don't baby my cashmere too much and give it a hand wash when I get home, it's more durable than you think. It's travelled all over the world with me ( I have two weights I rotate through depending, this trip I'll pack one and wear one), and they've lasted over a two dozen trips and ten years. One is looking a little threadbare and I have just replaced it with a new White and Warren diagonal topper, and it's making it's debut trip this time. I like that they have some history behind them and I don't mind the wear if they're getting used, it's like a patina. If only they could talk...
As for the plane loos, I'm with you Angie, I do my best to stay out of them! If I'm changing I'll do it at the airport.
Jennifer, you have this down to a science, thanks for all the excellent tips!