What to read to better understand Tolkien?

This winter I reread Lord of the Rings for the first time in at least a decade (third or fourth time overall) and I am 20 pages from finishing the Silmarillion for the first time.

I’ve read the Hobbit at least a dozen times (currently halfway through it with my five year old) and I’ve read the Children of Hurin (when it was first released) and I will likely read the other novelizations of long silmarillion chapters later this year, but I think I’m going to take a break from the man himself.

It’s been a delight, but it’s also got me curious about Tolkien’s influences and what the man himself enjoyed reading.

I had a Greek gods phase as a kid, like many, so I certainly recognize some pulling from Greek and Norse mythology. Of course there’s lots of Shakespeare, and while I don’t know if he’s confirmed to have read Lovecraft I’ve read a bit and the Nameless Things and Void Beyond the World certainly have some of that flavor.

What else would you recommend to understand Tolkien a little better. Is Beowulf any fun for a modern reader? Where is a good place to start with Arthurian Legend (I’ve thought of giving the once and future king a shot which is contemporaneous to Tolkien?)

In short: what do you read around Tolkien to better understand his works.

Edit: thank you for all the excellent suggestions! Seems like Le Morte D’Arthur and The Prose Edda are the most recommended so I’ll probably give those + Beowulf a shot, and when Winter (aka Lord of the Rings season) rolls around I’ll probably check out Letters and On Fairy Stories.

Also to everyone who mentioned the Bible: I’m a lapsed Catholic but I took it pretty seriously when I was young so I’m all set on that front lol.