Here are the contenders, over which I slaved for an embarrassingly long time. And here is the problem: I don't think I like any of them now, except for Llewellyn, and I can't really have that one because this kid is also going to have a four syllable double-barrelled surname, and filling out forms is tedious enough.
So which do you like, and alternative suggestions also welcome. The Welsh thing is coincidence, it doesn't have to be Welsh.
Frederick Rhys
Frederick Llewellyn
Frederick Owen
Frederick Hugh