Everything in my Bumpverse (Things That Go Bump in the Night and its sequels) is fluffy domestic Spuffy - well, except for the angsty stuff in TTGB, but it comes out happily. Many or most of the short sequels were written for Schmoop Bingo prompts - very fluffy.
My Always Wait For You is technically domestic, but they aren't together for all of it, so may be more angst than you're looking for. I Know You, II, a sequel to Prologue to Life/I Know You is Spike and Buffy working their way into a domestic relationship. It's shorter sequels take place after they've settled in. It's not about the domestic stuff, though, so probably not what you're looking for.
Of course, I presume you've already read Barb's epic fics? A Raising in the Sun, Necessary Evils, A Parliament of Monsters. Every story set in the Barbverse (after Raising) is domestic Spuffy. Which doesn't mean there isn't angst and bad stuff, but there's also lots of just being together and raising a family type stuff.