Frederic. I prefer it without the k; I had a relative with it spelt that way, nice old retired legal dude with lots of good stories. I would probably team it with some dull-but-sturdy family name, but for some reason
Frederic August just popped into my head, perhaps because you've mentioned it before? I like it.
Fred is fine, it's comfortable and friendly.
Other Freds:
I kind of like
Manfred and
Winfred, but I'm not sure they'd be great names to have if you were an actual boy.
Alfred I prefer in full, but
Fred for it might be a nice way of avoiding
Alfie which is tooth-gratingly awful imo.
Wilfred is handsome, but also a bit limp somehow. Wilting
Wilfred.