Thanks Pasi, maybe I post another shot that includes the boobs

Anthony, thanks a lot. I see your point regarding the calves and will have an eye on that next time I do s.th. similar. There might be a risk though that it gets too bony. Personally I like it the way it is.
Thank you very much Armando.
It gets easier with some practice , why did you find it hard ?
For a lot of reasons

here are some of them
- you described already a few i.e. there is a certain pressure not to fail that is higher as usual (I am not a pro)
- the working speed has to be kept up at a pace that is acceptable for both, model and photog
- the "arrangement" of the model has to be done with words. Touching is not adequate in my opinion.
- keep up a friendly, constructive and yet productive atmosphere (a lot of talking, joking, being serious when required, music etc.)
- provide the required infrastructure (again I am not a pro and I did it at home which required preparations)
- decide what is to the advantage of the model and what isn't in order to avoid disappointment (imho that's the only thing where it is harder to shoot a friend than an anonymous model)
- It is not a good idea to check the technical issues for half an hour and then curse and start all over again (it was my first shooting using 3 speedlights and i silently cursed quite often

I could go on much longer but have to leave now. I guess some of these points apply to all Model/Studio shootings but someone lying naked in front of you does not necessarily relax things

again, thank you all I appreciate you comments and hints a lot!
Chris