This is, academically speaking, a thorny mess. There are very few sources from England that describe paganism, and no sources from England which describe paganism uncontroversially. This is partly because Christians in England did not bother to write about paganism (except in very abstract terms that are essentially useless for reconstructing actual pagan beliefs). It may go deeper, however -- we do not know how pagan England was before the missionaries from Rome arrived. In fact, Christianity survived and thrived in Wales during England's 'pagan' period, and there is some evidence that Christianity survived in parts of England as well. Robin Fleming (in a book that you simply must read, if you're writing fiction about this period: Britain After Rome) suggests that paganism was something the elites played up in the seventh century; but what ordinary people believed -- Christian, pagan, or something in between -- is almost impossible to say. It's a true mess.

Older scholarship on 'paganism' tended to treat all Germanic-language-family-speaking people the same. This was based on an old (and incorrect) belief that people who shared a language also shared cultural and religious traditions. In fact, it's more complicated. But older scholars thought that you could take 13th century stories about Oðinn from Iceland and combine them with 1st century descriptions of 'Germanic' people in Tacitus, mix in some archaeology from Northern Europe, and come away with a picture of 'pagan' beliefs that was true for all Germanic peoples in prehistory. That's, honestly, just bad history -- we know now that beliefs and practices varied widely across time and space (even if we can't always say what a specific group of people believed), so you can't collapse Scandinavian myths into English beliefs and hope to have anything but a fantasy. That hasn't stopped scholars like Lotte Hedeager from writing books like Iron Age Myths and Materiality, which do collapse beliefs across time and space in very problematic ways. I would advise you to approach anyone who paints one region's religion onto another uncritically with a large dose of skepticism.

That said, we know a bit about ordinary people's folklore in Anglo-Saxon England. Karen Jolly has a great book about healing medicine in Anglo-Saxon England, and these magical charms are weird and full of folk magic that clearly has its origins outside Christianity. People in England also had beliefs about elves, monsters, dragons, and perhaps re-animate dead bodies -- you can catch glimpses of these in the names they gave hills, and the stories they told like Beowulf. Alaric Hall has written at length about elves in Anglo-Saxon England. His book is mostly philology, and as such is a very difficult read; but if you sift past the technical word studies, you can get a sense of the kinds of beliefs people may have had about these supernatural creatures. These beliefs weren't strictly pagan -- we know about them from Christian sources, and Christians seem to have believed in and used folk remedies, magic, etc without any hesitation. Elves in the hills were as real to Christian Anglo-Saxons as quarks and neutrons are to us today: something whose existence we accept as a matter of course because experts who know how the world 'really' works confidently assure us they're real. Sarah Semple has a good discussion of fear of monsters in barrows in this article.

In addition to this, there's the archaeology. It's really hard to say whether archaeological practices were necessarily pagan, but they do reveal a lot about beliefs in magic, the supernatural, the boundaries between life and death, etc (some of which was believed by both Christians and pagans at the time). Martin Carver has edited a good volume on archaeology and belief, and you can find a pdf of it online with a little googling usually.

My recommendation is that you avoid the 'big' stories (Ragnarok, etc) and try to work in smaller stuff. Add in a few healing charms from Jolly's book. Throw in some fear of elves, or monsters living in barrows. Base the stories your characters tell on the lesser-known bits of Anglo-Saxon poetry (the Fight at Finnsburg in Beowulf, rather than the story of Grendel himself; the story of Waldere; etc). Mix in votive, spiritual practices that we've found in archaeology, some amulets and superstitions, and have a cunning woman heal someone who is ill.