Beauvais No.195 is a lovely soft sage-green, but Mylands sits at the premium end and not everyone wants to pay that for a whole hallway or a couple of bedrooms. The good news is you've got three genuinely close matches, all cheaper.
COAT Yard Party is the pick of the bunch at ΔE 1.8 — that's very close, well inside the threshold where most people can't tell two colours apart on a wall. It has an LRV of 53.1, so it reads as a comfortable mid-tone green. COAT is water-based, low-VOC and dries quickly, which makes it a doddle for DIY.
Crown Sow Good is next at ΔE 1.9 (LRV 51.1), a touch deeper on the wall but still a faithful match. Crown's trade emulsion is solid, widely stocked and properly cheap by comparison.
Dulux English Mist 4 comes in at ΔE 2.1 (LRV 56.6) — slightly lighter and the furthest of the three, though still very close. Worth a look if you want a hair more brightness in a north-facing room, and Dulux you can grab almost anywhere.
The "but what about" here is finish and depth. Part of what you pay for with Mylands is that chalky, pigment-rich body — their Marble Matt has a real richness to it. The dupes match the colour beautifully, but a budget contract matt won't have quite the same depth or wipeability. If that matters, spend the saving on a better finish: Crown's Clean Extreme or Dulux's washable lines give you durability without the Mylands price tag.
My advice: order sample pots of all three, paint them next to a Beauvais No.195 sample, and view in daylight and lamplight. At under ΔE 2.5 the difference is marginal, but greens shift more than most colours under artificial light, so always test before you commit a full tin.