Go for Dulux Fine Cream. At ΔE 0.7 from Paint & Paper Library Stone I, the gap is so small the eye can't pick it out — anything under ΔE 1 counts as imperceptible. On a wall, side by side, you'd not be able to say which was which. Fine Cream sits at LRV 88.8, so it's a soft, light, barely-there cream that holds onto a touch of warmth without going custardy.
If for whatever reason Fine Cream isn't in stock or doesn't come in the finish you want, Dulux Apple White is your back-up at ΔE 1.3, LRV 86.6. Still very close — comfortably under the 2.5 threshold where most people would notice a difference — just a whisker fresher and a touch less reflective.
Now, the honest bit: matching a Paint & Paper Library colour into Dulux is usually about saving money or convenience rather than getting a better paint. P&PL's pigment load and the depth you get from their Pure Flat Emulsion are part of what you're paying for, and a colour-matched Dulux tin won't replicate that body and chalkiness exactly even when the colour reading lands bang on. Where it matters most is sheen — a flat P&PL finish and a Dulux soft sheen will read as different colours in raked light even at ΔE 0.7, because sheen changes how the colour bounces.
So match like-for-like on finish. If you loved Stone I in a flat matt, put Fine Cream into a flat matt — don't let the merchant talk you into Diamond Matt and then wonder why it looks off.
Practical tip: always order a sample pot of the Dulux match and brush it out next to your original Stone I swatch before committing to litres. Colour databases are excellent, but your light, your wall and your primer all have a say.