Blue Blood is a cracking deep moody blue, but Paint & Paper Library sits at the premium end, so I don't blame you for hunting a cheaper tin.
The standout match is Dulux Pebble Drift 1 (LRV 15.9), which comes in at ΔE 1.3 from the original. That's below the threshold where most people can perceive a difference side by side — essentially the same colour for a chunk less money. Get it in Dulux Heritage or the Trade emulsion range and you'll have a tougher, more wipeable finish than the standard retail line, which matters with a dark colour that shows scuffs.
If you'd rather a low-VOC, water-based option with proper depth, COAT All Inclusive (LRV 16) lands at ΔE 1.5 — still very close, and COAT's flat matt has a lovely chalky body that suits a colour this dramatic. It's also self-priming-ish over previously painted walls, so fewer coats.
The third option, Crown Runaway (LRV 17.5), is a touch lighter and reads slightly less saturated at ΔE 2.4. That's still a very close match, but it's the one I'd reach for last of the three — it'll feel marginally softer on the wall.
One thing to flag: deep blues like this shift hard with light. In a north-facing room Blue Blood and its matches go properly inky and can feel cold; in a south-facing room they warm up and show more of their character. Always sample the actual alternative you're buying — don't trust the original swatch to tell you how Pebble Drift will sit on your wall.
Practical advice: with any colour this dark, prime patches and bare plaster with a tinted grey primer first. It saves you a coat and stops the finish looking patchy. Buy a tester pot, paint two coats on lining paper, and live with it for a couple of days before you commit.