I would argue that you don't have to explicitly say things like "it seems" or "it looks to me," etc. because everything in first person is inference or "after the fact" especially if it's told in past tense. It's perfectly okay to say "Mary was unhappy" because a) it's either clear that the narrator is making a judgment based on what he observed, and/or b) the fact was confirmed later (it's told in past tense).
So, there is flexibility when it comes to first person, especially in past tense/retrospect. Even "she thought" would be acceptable if, within context, we understand the narrator is either making a judgment or reporting a later-confirmed fact.
What is not acceptable is things that are clearly out of the narrator's perspective and there is no indication (or context) how the narrator would know about it. An extreme example:
I met Mary for lunch today. Little did I know John was planning to kill me 3000 miles away in New York.
Without context, that's a violation of POV. But if we add the necessary context, it's still good:
I met Mary for lunch today. Little did I know John was planning to kill me 3000 miles away in New York, until Jane called and told me about the plan.