Are you looking for survivability or sustain? Cause those are 2 different things.
For survivability, I recommend Catalyst, which you can build into a RoA or BV later on.
For sustain, I suggest Chalice or Philo stone.
Philo definitely if you're having an issue with survivability too. Because that means you aren't going to be able to last hit well, so standing back and getting some extra gold when you regen is useful.
Chalice seems like the way to go.