I've been looking for a first hand account of the early medieval period in Northern Europe. I know written history from this area doesn't really go back much further than that. If anyone can give me any information on first person accounts only, I'd greatly appreciate it!
Do you want first person accounts or the oldest accounts? I doubt those two are going to be the same.
Some of the oldest sources will be saints' lives, usually written by biographers/hagiographers long after the saints were dead. See for example Adamnan's Life of St. Columba for Scotland: http://legacy.fordham.edu/halsall/basis/columba-e.asp
I am not completely certain in regard to personal accounts, but I know that the oldest Danish chronicler is Saxo Grammaticus who wrote Gesta Danorum during the reign of Valdemar the first. In regards to England, if that is considered Northern Europe, you might be interested in William of Malmesbury who wrote about William of Normandy and his sons in their time. One more you could be interested in would be Bede, the "father of English history" who wrote the Historia Ecclesiastica Gentis Anglorum (one I know little about personally). Lastly you might be interested in the Icelandic Sagas such as Egils saga, but there really is a lot of them.
These are a few suggestions and there are plenty more, but what you exactly need is unclear to me in regard of exact place and time period. Moreover the 'first hand account' part is a little problematic since only few were able to write and read and therefore the chroniclers sometimes got the material for their stories from other scholars or chronicles.