Mellow greetings,
just wanted to thank you again for the recommendations; after having read the FAA handbook I got myself a copy of Cyclic & Collective and it's indeed what I was looking for (my beginning the second part for professionals now might be a bit over-the-top, but I paid for the whole book, and it's just too interesting a read).
(Of course could not resist to have another go either, and this time there were actually some limited periods where the helicopter pretended to do what I want (which was mostly staying still some feet above the ground). What was less encouraging was the fact that when I wanted to put it down for a break, the instructor had to take over again. Quite nice and steady descent (in perfectly calm conditions, of course), but just the last few inches above the ground seemed to be infested by the curse of the wobbly copter despite (or because of?) all my efforts to make a soft touchdown without any horizontal motion. But then, according to the instructor, I am not the first newbie befallen by that curse.)
Absolutely fascinating flying machines, in any case!