Myriam, you might be right. It looks a lot like the S. grandiflorum.
I got this plant from a friend and she lives, just like me, near the German border, so I tried to find the plant in the 'Bildatlas der Farn- und Blütenplanzen Deutschlands', but all the white and low growing Symphytums had different leaves. And the leaves of this plant look similar to my plant.
