OK, you'd like to read on the detailed political history of the 7th century Britain, such as the world of Bede the Venerable (I assume you might also like to read/ have already read the English translation of his HE).

I'm sure that proper Anglo-Saxon special flairs like /u/BRIStoneman and /u/Steelcan909 must have more to say on OP's topic as well as much better selection of the recommended literature, but at least I can also suggest some basic books below:

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(Entry-Level)

• Charles-Edwards, Thomas. 'Nations and Kingdoms'. In: After Rome, ed. Thomas Charles-Edwards, pp. 23-58. Oxford: OUP, 2003. Short Oxford History of the British Isles: is the easiest as well as in some depth read to give some up-to-date overview of the post-Roman political geography up to the ascendance of King Offa of Mercia. Robin Fleming, Britain after Rome: The Fall and Rise 400 to 1070 is a generally recommended excellent general work, but it might has too little details on the political dynamism of the 7th century.
• Higham, Nicholas J. & Martin J. Ryan (eds.). The Anglo-Saxon World. New Haven:Yale UP,2013: is must read for you, I suppose. Edited by one of few experts specialized in Early ASE, with a brief introductory 'sources and issues' essays on the primary sources.
• Yorke, Barbara. The Conversion of Britain: Religion, Politics and Society in Britain c. 600-800. Harlow: Pearson Longman, 2006: offers a balanced overview of the Christianization process of all the Britain, often intertwined with politics, at that period.

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(Intermediate)

• Bassett, Steven (ed.). The Origins of Anglo-Saxon England. Leicester: Leicester UP, 1989. Studies in the Early History of Britain: is a classic collection of the essays on the formation of the kingdom in ASE, though focusing rather on the structural aspect of the government than on the detailed political events.
• Davies, Wendy. Wales in the Early Middle Ages. Leicester: Leicester UP, 1990: gives the standard overview of early medieval Wales, though not so much in the 7th century.
• Higham, Nicholas J. An English Empire : Bede and the Early Anglo-Saxon Kings. Manchester: Manchester UP, 1995: argues on how we should read the descriptions of Bede from a critical (rather very skeptical?) point of view, to look through a complexity of Early Anglo-Saxon England.

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(Advanced)

• Charles-Edwards, Thomas. Wales and the Britons, 350-1064. Oxford: OUP, 2013 (pbk: 2014): is very heavy in content as well as as a physical object, but this is almost only the very detailed history book on Wales in the Early Middle Ages, making fully use of Welsh-British sources like inscriptions.

/u/y_sengaku has done a great job of providing a good reading list.

I'd also suggest:

Barley & Hanson (1968), Christianity in Britain 300-700

Curta (ed.) (2006), Borders, Barriers and Ethnogenesis: Frontiers in Late Antiquity and the Middle Ages

Davies, Halsall and Reynolds (eds.) (2006), People and Space in the Middle Ages, 300-1300

Petts and Turner (eds.) (2011), Early Medieval Northumbria: Kingdoms and Communities, AD 450-1100

Reynolds (2013), 'Archaeological Correlates for Anglo-Saxon Military Activity in Comparative Perspective' in Baker, Brookes and Reynolds (eds.), Landscapes of Defence in Early Medieval Europe

Yorke (2001), 'The Origins of Mercia; in Brown and Farr (eds.), Mercia: An Anglo-Saxon Kingdom in Europe

Charles-Edwards (2001), 'Wales and Mercia, 613-918' in Brown and Farr (eds.), Mercia: An Anglo-Saxon Kingdom in Europe