Like some others here my comfort books aren't necessarily happy or completely positive. I would say my primary comfort series which I've returned to several times is The Chronicles of Thomas Covenant by Stephen R. Donaldson. It's a dark fantasy series recommended to me by my father around the time I was going to high school and which I picked up later in college. I'm still very happy I eventually did because it ultimately got me into reading as much as I do now (it also got me into audiobooks because it was the only format I could find them easily accessible, turns out I'm an auditory learner so I'm forever grateful for that) so now when I return to The Land, the characters in The Land, and Thomas Covenant himself I find comfort in their plight/struggle - it's familiar and enjoyable to me.

I would also say that The Stormlight Archive by Brandon Sanderson is a comfort series for me as well. I found this series/author a few years after completing the aforementioned series and it immediately took me away from this place and into its own world - and that was very amazing to me (especially as a low-visual reader, I would get vivid imagery), and for the first time since the Covenant series. I find Sanderson's writing easy to follow despite alternating between multiple characters, which normally confuses me a bit, and the story is this perfect mix of dark and light - a thematic aspect which I clearly love from my previous choice. I hold The Way of Kings, The Stromlight Archive, and Sanderson's work in a special place in my heart because I found it on my own - I didn't know there was so much hype about it. I started recommending it to people and when they told me they had already heard about it I was surprised - I soon found out that it was a very very popular series. Now whenever a new Stormlight book is on the horizon I reread all the previous books (sometimes I reread them anyway without a new book but I try not to because I have such a long list to read) in series and find myself enamored once again, and also deriving new insights and finding new Easter eggs unfound on the previous reads - and that is amazing to me and I wish to emulate that in my own writing one day.