In previous Souls games, there is usually at least 1 vendor in the hub area. I've read online that the Handmaiden fills this role in Dark Souls 3 and sells all kinds of useful things, including garments to cover my lower body. But I've run around Firelink for an obscenely long time without being able to find her.
Where is the Handmaiden?
Seriously, this loincloth is getting real drafty and no enemies are dropping pants.