There's an alternative system from 2007 (oh, how time has moved, oh, how old you are now True20!) - Baduin's Alternative Damage System and then some modification to that here that inspired me to putz around with what ended up being a Damage Track on a character sheet I was planning to use.
My main draw to the system was simply missing the change to roll damage! It's ingrained, I guess. Your Toughness becomes a static number, which then has 5 degrees added to it for how badly you're hit, depending on the damage your attacker rolls.
So, here's the whole character sheet, note the damage track:
Our squishy Adept with (static) Toughness 4 compares that on the table. He's already filled in the large upper boxes on the Damage Track with values 9, 14, 19, 24, 29.
The 13 damage rolled is between 9 and 14. Our Adept is Hurt, and fills in a box - we're looking at the Damage Track values as needing to be Equal To Or Greater Than. (essentially, everyone's base Toughness is 5 before CON modifiers or armor)
- The Adept is hit for Damage 4. Less than 9, he is unscathed.
- Damage 12 - second box under Hurt is filled in.
- Damage 15 - first box under Wounded.
- Archers take aim, and he's hit for 7 and 9. He fills in the last box under Hurt from the Damage 9 arrow. The first one winged him, a minor scrape.
- A sword-strike for 11 - his Hurt boxes are full, so he fills in the second Wounded box, the lowest box he can take. He's in trouble.
- Another arrow volley - 15 and 16. The last Wounded box is filled in, and, since he's out of those, he has to fill in the Disabled box. He's in trouble, and limps off to cover.
Note squishy folks are squishy - an Ogre, perhaps, swinging a club, could be rolling d20+7 for damage - if that Ogre pops out a roll of 18 or better, our Adept is dead.
This system doesn't really address the 'spiral of death' that happens with the Toughness save as written - it helps a little in that you're not penalizing a poor Toughness save with further penalties as you get damaged, but there can be a sudden drop-off if you're in a long, low damage fight, and you're just simply running out of boxes.
In fact, I wrote a little Perl to give me some math on this back when I was working on it.
The Attacker's to-hit is +4, and so is his damage. The defender's Defense is 4, as well as his Toughness. A battle of average men. This was 100,000 simulated battles, I think?
4 Attacker vs 4 Defender, 1d20+4:
Total Hits: 809410
Average Hits: 8.0941
Dying Hits: 40338 4.98363005151901%
Instadeath: 0 0%
It takes about 8 hits, if that defender just stands there and takes it, to get killed. The attacker drops the defender to Dying on 1 hit 5% of the time (he rolled a 20!) That program didn't take into account any further penalties from the damage conditions.