Dáibhí Ó Cróinín's Early medieval Ireland, 400–1200 and Donnchadh Ó Corráin's Ireland before the Normans are both excellent surveys that cover the social history of early medieval Ireland with descriptions of dress, diet, family structure etc. In terms of primary sources, early Irish literature can shed light on an idealized aristocratic vision of society and frequently describe elaborate noble dress in detail. However, they aren't really reflective of society at large which is something to keep in mind if you decide to use them.

It would probably be a good idea to look into archaeology as well. I haven't personally read it, but I've heard good things about Nancy Edwards' The Archaeology of Early Medieval Ireland which goes up until the Viking Age. Be careful about any scholarship older than the 1970s-80s because they relied heavily on legal texts and Anglo-Norman ethnographic works to paint a portrait of Irish society at the expense of archaeological data. This is problematic because legal texts probably represent an idealized picture of society and because those Anglo-Norman texts were fairly derogatory and contained highly exaggerated depictions of Irish customs.