Dueling flavor addition, help wanted

[ParasocialTroop]

I've got an eastern themed campaign using pathfinder 1E/DnD 3.5 rules. I'm interested in introducing some more Wuxia and cinimatic elements to the campaign. One thing I want to do is add in something to spice up a martial arts duel as I have several melee martial artists at the table.

The goal: Easy to implement mechanic that adds depth and/or interest to a 1v1 melee fight. Something that is dynamic and can change round to round. Ideally something that there are multiple options for.

Constraints: I don't want to change normal mechanics too much. I'm focused on a potential duel and mostly for melee combatants, but if we make something more robust that'd be fine.
I want it to influence the combat, but also not overshadow what characters are optimized to do in combat (as my players have put effort into making characters that can do certain things).

Initial idea:
The new mechanic would be to include a round in between combat rounds where you can do something that is not combat to give you an edge in the next round. This could be representing setting a strategy, maneuvering terrain or switching combat styles, something to give you an advantage.
Combat map rules is theatre of the mind since the assumption is that a melee martial character wants to be still and do full round actions anyways.

My questions: What should the mechanic be? Maybe an opposed check with an attribute of the character's choice to represent what they're trying to do. Or opposed skill check. Any of these seem very coin filp-ish.
Maybe a rock paper scissors sort of thing with the 5 elements. Feels like a psyche out, but really it is just randomness.

What should the effect be? A flat bonus to d20 rolls. A bonus you can use on one roll? Winning initiative for that round? Advantage (5e) for a certain roll?



Alternatively are there other systems that can work well with d20 that have compelling dueling rules?