You could simply alter the parry system.
Back in the day, there was a time when I decided to add an active parry to 1st ed AD&D combat. It was a "to hit" roll, with whatever bonuses you would normally get. You were essentially attempting to hit your opponents weapon while they were trying to hit you... which is what parrying with a weapon seems to be all about.
The simplest way to handle this was to let the higher roll win. If your roll plus bonuses exceeded your opponents, then you blocked their attack. If their attack roll and bonuses exceeded your parry attempt, then that roll was applied to your AC to see if they actually scored a hit and caused damage.
Yes, this made combat a drawn out experience, much like the swashbuckling sword fights we see in the movies, were 95% of all the sword swings would hit the opponent's blade. Yes, it was an active thing, where if the PC did not say "I'll parry that" at the time of an attack, they did not get the option to parry it. It was never an automatic thing.
Sure.... for some PCs, with their incredible strengths and amazing magical weapons, in melee combat they were virtually untouchable. There were always spells and catapults and falling flaming trees to kill THOSE guys... but that's another story.