So finally: The Bezier curves in the cross section is the better choice!
That works easy and perfect.
By the way: In earlier versions mesh surface creation was sometimes a problem cause the curves were splitted. (like the shape in the picture, the outline separated in several curves)
Todays the merge curve does a perfect job, and it works perfect! (I select merge curve, simply select the edges and it creates the one curve! = fantastic)
Thank you!