Picked up a S red belt, silver buckle, and another v-neck (red).
If S doesn't work for me (I wear 29-30 in pants, might be too big) and works for you, I can sell it to you and order an XS.
My first Frank & Oak order came in today, and their smallest size buttondown is unfortunately too large for me (their $50 blazer is alright, though). If y'all are able to get a better range on sizes (which based on your tees, you can), then I'll try that out. Until then, Uniqlo XS will be my go-to for low cost buttondowns.