Borrowed Light is that pale, slightly chalky sky blue that reads almost off-white in dull light and properly blue when the sun hits it. Lovely thing — and a popular one — so it's no surprise people want it for less.
The standout match is Dulux Celestial Cloud 6 at ΔE 1.2 (LRV 70.9). Anything under ΔE 1 is imperceptible and under 2.5 is very close, so at 1.2 you're looking at a difference your eye genuinely can't pick out side by side, let alone across a room. Dulux Heritage or the standard Dulux line in a quality finish will give you a hard-wearing wall for noticeably less per litre than F&B.
Next is Crown Watermark at ΔE 1.7 (LRV 65.6). It's a touch deeper — that lower LRV means it'll hold the blue a little more in shade and won't bleach out to white quite as readily. If your room is bright and south-facing, that can actually be the better call, because Borrowed Light itself can go a bit washy in strong light.
If you'd rather stay in the modern eco camp, COAT The Good China comes in at ΔE 2.4 (LRV 73.2). Still very close, slightly lighter and cleaner, and COAT's a self-priming, low-VOC paint that does a proper job.
The usual "but what about the F&B finish?" question: the magic of Borrowed Light isn't a secret pigment, it's just a well-judged colour. A good Dulux or Crown match in a decent matt emulsion will look every bit as good on a wall. Where F&B earns its keep is depth in their dead flat and estate finishes — but for a pale blue this airy, you won't miss it.
Buy a tester of Celestial Cloud 6 and Watermark, paint A4 patches on two different walls, and live with them for a couple of days before committing. Light direction will decide it.