Sto bene, grazie, FL, ma sono molto stanca!
I think the bechamel puffs up as you say, BillyB, if you put an egg in it - which is not done in lasagne here, generally, but perhaps our friend from Bologna might intervene here with his take on it. Otherwise bechamel doesn't puff up, at least not in any of the lasagne i've ever eaten in restaurants.
I guess also it depends on what you mean by heavy - the lasagne with many layers of bechamel, with all the butter and whole milk that entails is quite heavy in terms of being fatty - also in that it doesn't puff up, it is dense, and physically heavy, that is it has a denser mass. Also note that there is not one layer of bechamel, but many, one layer of pasta, one of bechamel and one of sauce, one layer pasta, bechamel, sauce, etc.
In the traditional american lasagne, which is probably from some town somewhere in italy, I'm guessing sicily but may be wrong, there is a single layer of ricotta, whcih is low in fat, and some parmigiano, which the italian one also has, and the rest is tomato sauce. It's not, like the bechamel version, with a layer of ricotta between each layer of pasta.
So i sort of prefer it with ricotta because I'm not crazy about a "first course" that's so intensely heavy. (Remember, people don;t just have lasagne here, it's just a first course, before the main dish!). Groan. So, i ask, why are all these italian women so &%#$@ skinny? Probably all the smoking.