The Reach, the religious center and home to the Grand Citadel was rules by House Gardener before Aegon took over. This region is also a huge agricultural one, and one of the richest lands in all of Westeros. The fashion I based this off of was Italian. So. So let us start.
Men wore a linen chemise and loose-fitting drawers under their outfits. Over this, they wore a plain long sleeved linen or woolen tunic that was knee-length or longer. This was cinched with a belt on the waist. Over all of this, they wore an outer tunic with shorter sleeves or one that was completely sleeveless, and the highborn lords had these embroidered with fancy styles at the hem, neckline, and wrists. Loose-fitting hose were on the legs, and these were held up using garters. When it was chillier, men would wear rectangular or circular cloaks which were fastened at the shoulders with brooches. Leather shoes or boots were common. (Third photo is example of cloak, and NOT the fashion)
Like many other regions, highborn lords kept their hair long (shoulder-length) and either curled it or kept it well groomed. Smallfolk men would keep their hair short, and protect it while they were working with a coif (linen cap). The religious septons or septons-to-be had a tonsure hairstyle, which is where only the top of the head is shaved, and the rest is growing around it like a halo. Unlike other regions, beards were either VERY well groomed, and a lot of men were clean-shaven. Examples of coif and tonsure below.
Under their outfits women would wear linen chemises, which had long sleeves. Over this women layered their kirtles or tunics to keep warm. These were floor-length and rather loose fitting. Mantles and cloaks were worn over this all. Belts were common, and held a girl's possessions on it. Smallfolk women would just wear wool or linen. Higher born ladies could afford silk and fur lining in their cloaks. Simple leather shoes were worn.
Women's hairstyles were surprisingly more simple than expected. Their hair was kept long, and oftentimes braided. Highborn girls could incorporate ribbons into their hairstyles. Another popular style was to wrap the braids around the head or into buns, which highborn ladies then styled with a sheer silk veil. Married women once again had to cover their hair, and did so with veils that were wrapped around their head twice, and could have a chin strap.