The simplest subclass.
You're tougher and hit harder.
Level 3
Tough Cookie.
Increase the size of your Hit Dice by one step (d6 to d8).
Level 7
This Guy Won't Stay Dead.
(1/Encounter) When you drop to 0 HP, regain 1 Hit Die.
Level 11
Vitality.
(1/Safe Rest) Add your level to the result of any Hit Dice you roll.
Level 15
Fight All Day, Fight All Night.
Whenever you roll Hit Dice, reroll any 1s.