The order you apply Poison and Maternal Comfort doesn't matter, since between turns a Pokemon is not evaluated for KO until all between turns effects are applied.
So, apply poison damage first, its now at 110 damage = to its maximum HP.
Now, apply Maternal Comfort, its now at 100 damage.
All effects applied? OK, NOW evaluate - is it KO'd? No.
That said, since you control the PKMN you may apply the effects in whatever order you want... just don't check for KO between turns until all effects are complete.