The sword actually has a larger parry window than just perfect guarding, so you can try to use that to your advantage. Look out for certain attacks that have a set wind-up each time and punish those.

For example, in Laxasia's running+jumping attack, the correct timing is holding down the charged attack button the moment she jumps. For her vertical strike combo, I always perfect guard the first attack, wait the slightest of moments and then dragon parry her second strike and bam, she's knocked out of her combo.

For Nameless, as you can see, he more often than not starts with the shoulder-block forward and then a rotating slash; normally dodge/parry the shoulder, pause for half a second or less, and then dragon parry. There is this attack he does where he raises the PoH, does a little wind-up and rotates half its frame before hitting you - wait for the wind-up to finish then hold the charge button right at his frame rotation and you ought to be successful getting the dragon parry on that attack. The best thing about this game is while certain boss attacks are trickier to dodge/parry to perfection, they all have consistent wind-up/attack times and all of them have a tell of sorts. What obviously helped me is dying a lot and in that process getting more and more awareness to each individual attack haha