One way to do it is to keep the stamina/lifeblood system in place, and if you take lifeblood damage during combat, you must make a fort save or go down a step on a condition track.
EDIT: Another idea is to adapt 'Force points' into T20 as 'luck points'. You get a number of them per level, and they're a finite resource. Once spent, they're gone, until you level up (and leveling isn't a major focus in T20 I think, not as much as in other d20 systems) The feat 'Dumb Luck' can also be really useful (er, more useful than it already is I mean) by turning the 1d6 into a 1d8 instead.
Having played Saga Ed for about 8-9 months, Force points are often the difference between hitting someone or failing otherwise. This works in SW, but does it in Traveller? Well, maybe that's a difference in people's views on what should constitute the gameplay, but whatever makes the game fun IMO is my attitude. Incidentally the SW game I play has house ruled Force points to where they're reusable, and I don't think this is the way to go at all - even for SW. But I'm just a player.
Incidentally, Dumb Luck by itself is already a pretty disgustingly great feat to take. Once per week, you can reroll a failed check, save or attack, or turn a successful check, save or attack into a critical success (er, I think that only applies to attacks really? Only attacks have criticals). That's actually more akin to Saga Edition's Destiny point system. The proviso is the next week you can't use Dumb Luck at all, but hey you spend a week in jump space, so that's not a problem either!