As for allowing a Defend Interrupt Action and also an Attack, you might want to look at the various Feats that exist around Defending already.
Namely there are Defensive Reflexes, Defensive Mastery, Sentinel, Battlefield Punisher, Attack Redirection and most notably Battlefield Retribution, which allows a character to deal Damage with a Defend Interrupt.
Also note that Shields (or any other Weapon with the Defensive property) give Advantage to Defend Interrupt in addition of granting +1 to Guard, which is also the reason why I included Defensive Mastery.
A more defensive fighting style also exists, it’s the act of making a Defend Interrupt at all.
For a defensively built character this can be the usual path to take upon being hit while still actively contributing via things like Battlefield Retribution, but for an offensively built character this might be the last thing to do before being knocked out because they usually contribute differently.