Are there any thin short-sleeved knits that would go well under slacks in this late summer weather, when it's still hot during the day and cool in the evening?

As short-sleeved knits that are great to wear in late summer, I picked an open-knit bouclé knit and a checked PK knit blended with Tencel and silk. The bouclé knit has an open knit structure, making it great to throw on lightly, and the PK knit features button and collar details, making it easy to style with slacks for a neat look. Both are priced in the KRW 120,000 range.

For a short-sleeved knit design with a collar, I picked a knit top featuring a check pattern and metal buttons. It comes in 2 colors, burgundy and grey, and is crafted from a yarn blended with acrylic, Tencel, merino wool, and silk. Both colors are priced at KRW 129,000.

Here is the collared short-sleeved knit in the burgundy color you mentioned. The check pattern and metal button details pair neatly with slacks, and since it is made of yarn blended with Tencel and silk, it is great to wear in late summer weather. The price is KRW 129,000.