Have rolling modifiers on story & moderator approved items and give every character health based on their race, affiliation & profession.
Simply keep the /roll 20 as it is and just add the modifiers from item’s and your persona card.
It’s as easy as combining what we already have in terms of mechanics which are accessible to every player.
For damage-calculation I would go for a 3 tap mechanic, where the persona has several hitpoints (head, torso, limbs, mind, soul etc.) with each hitzone having a seperate hitzone and once that hitzone is depleted from it’s healthpoints it’s out and you will have to roleplay the consequences accordingly to what happened in combat, e.g. having an arm almost severed or having your skin burnt crisp by an offensive spell. Actual damage dealt would be either the difference in the fighting players dice result or a set damage by weapon type.
Fights would be as simple as deciding to either attack a hitzone, block a hitzone / dodge or parry an attack. You hit a /roll 20 and let’s say you get a 14, your opponent then has to get a roll that’s higher than yours to avoid or afflict damage. They /roll and let’s say they get a 10, subtract your result from that and that’s -4 = 4 Damage to the opponents hitzone, or a successful dodge, block and a parry could even subvert the damage to your opponent!
An example with modifiers could look like this.
You have a dagger that’s story approved to have a modifier of +2 on your attack rolls when attacking from up close and throwing.
You hit a /roll 20 +2 and let’s say you get a 9+2(11), you’re opponent then has to get a roll that’s higher than yours to avoid or afflict damage. They /roll 20 +4 because they are a burly dwarf in armor and let’s say they get a 10+4(14), subtract your result from that and that’s 3 = no damage dealt to the opponents hitzone, or 3 subverted damage if they were to parry.