While there is always more to be said, /u/BRIStoneman, /u/Steelcan909 and I posted a recommended book list both on early and late Anglo-Saxon England below for a while ago:
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BTW, while the concept of 'Heptarchy (Seven Kingdoms)' (together with 'Bretwalda') ultimately derives from Bede's description and have had a long tradition of its use from the 16th century, recent scholars tend to avoid its use, stating:
'......it obscures the complexities which lie behind the political development of each kingdom, and conceals the deep-rooted differences between the kingdoms which helped to determine their respective fortunes' (by S. Keynes, 'Heptarchy', in: The Blackwell Encyclopaedia of Anglo-Saxon England, ed. M. Lapidge et al., Oxford: Wiley Blackwell, 1999, p. 233).
It is also worth mentioning that some, especially young generation of researchers begin to prefer 'Early English' to 'Anglo-Saxon' to designate the period now, as explained in: Misnaming the Medieval: Rejecting “Anglo-Saxon” Studies. So, if you search on internet, to mind the choice of keyword will also make a difference to find more and more suitable available choices of books.
I'm not so good at checking the historicity of fictional works (and tend to evaluate historical fictions almost solely from a point of view of historical accuracy/ probability), so I'll leave the task of listing recommended historical fictions set in this area and period to someone else (sorry).