Bone China Blue is one of Little Greene's loveliest soft blues — that calm, slightly chalky mid-tone that reads gentle in north light and properly restful in a bedroom or bathroom. The good news is there are a couple of genuinely close matches that'll save you a few quid a tin.
The nearest of the lot is COAT::Lie-in at ΔE 2.2 from the original. Anything under 2.5 is very close — you'd struggle to tell them apart once it's dry on a wall, and certainly not from across a room. Lie-in sits at LRV 49.9, which is a touch lighter and brighter than Bone China, so it'll bounce marginally more light in a darker space. COAT is also low-VOC and washable, which makes it a sensible shout for kids' rooms and bathrooms.
If you'd rather buy off the shelf or have it tinted at the trade counter, Dulux::Steel Parade comes in at ΔE 2.6 (LRV 47.3). That's just outside the "very close" threshold but still a strong match — the difference is the kind of thing only a paint nerd with two brush-outs side by side would clock.
Crown::Gentle Blue is the furthest off at ΔE 3.6 (LRV 44.5). Still recognisably the same family, but it's drifting enough that I'd only go for it if it's what's already in your hand.
The usual caveat: a colour match is not a finish match. Little Greene's Intelligent Matt has a particular depth and chalkiness that the cheaper paints won't replicate exactly, especially in raking light. So before you commit, buy a sample of your shortlist and a sample pot of the real Bone China Blue, paint them side by side, and look at them at three times of day. That fiver settles the argument far better than any ΔE number.