HKB,
Congrats on the birkin. Black is a classic color, size 35 is perfect for you. You are worried about the slouch and the grain and the hardware. All these are really your preference.
Grainy and Matte.
Clemence and Togo both have the matte look, if you want it to be shiny, it's either box calf or cherve.
Clemence, Togo and Cherve are grained.. Box is smooth..
Grain is less scratch proof.. box on the other hand is totally different story (until the patina blends it in)
Slouch:
Do you like structured look or slouchy look?
Structure: Boxcalf, epsom and some other leathes might be better.
I also seen some ladies use the bagmate for organising their Birkin and that does help abit with the structure of their clemence bag.
But you also state you want 1 bag for life:-
I saw some of the ladies' bags here, Clemence and Togo are pretty good wearing and Togo is such a good workhorse. But I understand it is heavier than Clemence.
Boxcalf if taken care well, can last for generations.
GH or PH:
I wear mainly silver or white gold stuff, but I love love gold on black or any dark toned colors, it's a personal preference. PH may have a younger feel to it.
What's wrong with this bag? What is not making it tick for you? If you don't feel it, just pass it on. or another question, if you can SO again - what would you get?
HTH