I’ve been looking at getting a gambeson for fun (picture) and I am also planning on making an unconquered highguard character for my first character and so I was wondering if something like this would be appropriate as part of a costume / what can be done to make it more appropriate. I have taken a look at the look/feel section for highguard (+ the costumes section) and read the unconquered page but I am just slightly unsure about making an appropriate kit.
Many thanks!
Welcome to the Forums, Coati! 
That does look pretty good for Highborn Unconquered, being somber and severe but largely unornamented.
I can see adding a mantle and hood in your chapter colours, maybe a chapter sigil hanging off a belt… but that’s a nice gambeson!
You could add some slight colour contrasts in terms of trim at neck and cuff, perhaps? Silver or gold? Not too much, or it starts to look a little Dawnish.
I think what you have there is a good solid base, from which you can add a few accessories as needed, or keep it stripped down for fighting in.
Have you checked with the Highguard Facebook group?
Hallo!
Unconquered brief, best martial Highborn brief (who doesn’t like being someone willing to do stuff in the metaphorical dark so people can do their big Virtuous charges?)
…this is said as someone who currently plays in Highguard and has a character who used to be unconquered and has been (unsuccessfully) trying to move away from the role
Seconding @Geoffrey_Willoughby 's comment about adding a colur pop of a sash or cowl, as having something to pull up over your head when magical shenanigans are going on is Very Highborn
As example of what you can see as “lighter armoured” Highborn kit in field in combat
(photo from Krios, from the event just gone)
The two of us in the foreground- far left and centre- play opposite each other in Highguard.
The person in the centre has very classic “solid black, colour pop of silver and orange associated with chapter”
My kit (far left with the funny expression) relies a bit more on cut to come across as Highborn, but fulfills the same “vibe”
I would also, because events are getting warmer and full black in the not-very-shade-covered field is slightly toasty, suggest you look at some thinner basic blacks/colour pop layers in addition to the very nice gambeson above
Cotton and linen heavy items are your friend here, as there’s a lot of airier weaves that mean you can wear a lot of black and not struggle as much with the heat.
It’s a great base for your kit. Never be unarmoured, never be without a dagger. 
A hood is a great way to instantly ‘Highguardify’ any kit IMO. Something like this with some added white/red/blue trim (whatever your chapter alt colour is) would definitely make you look Highguard, rather than Dawnish in that gambeson.
Thank you all for responding!!! I’ve been meaning to do a sewing project to take a break from my larger one so I’ll give making a hood a go next (and actually use up some of my excess fabric as I accidentally bought 3m of black cotton and didn’t know what to use it in)
May I suggest a simple T-tunic for using up your black cotton? Always nice to have a spare base layer or two.
The incredibly useful Custom Smock Pattern Generator will draw up a custom pattern to your measurements, including dimensions for a good sized keyhole neckline (the trickiest bit to get right, in my experience).
