Despite finishing third in Group A, Northern Ireland will now have a play-off to look forward to in March as they look to reach a first World Cup since 1986.
Speaking after their 1-0 win against Luxembourg, O'Neill said: "I think at times we've been a little bit unfortunate with some of the decisions that have gone against us and also a little bit unfortunate with the players we've had unavailable to us with injury as well.
"But over the piste, we've made a lot of progression, and that gives us a lot of optimism for the games in March."
He added, "We've kind of nailed down our preparation, and one of the things we've been very, very consistent with now for quite some time is the system of play and what we're asking players to do.
"So, we're not coming in and changing dramatically what we're doing. It's a case of personnel, and sometimes we have to change personnel. But we'll be ready to play regardless of who it is, even though it'll be short preparation time."