The Stamford Bridge club finished their campaign with a 2-1 victory over relegated Cardiff City on Sunday and Mourinho immediately turned his attention to strengthening his squad for a championship charge next year.
After Craig Bellamy had put Cardiff ahead early in the first half, it took Chelsea until the 72nd minute to draw level through Andre Schurrle, and three minutes later they secured the win thanks to Fernando Torres.
The victory sees Chelsea finish four points behind champions Manchester City, but Mourinho's side scored 31 fewer Premier League goals - an area of obvious need for improvement.
"Finishing third is not a drama, it is a position we will have to accept in a transitional season," the Portuguese said. "We deserved to win (against Cardiff), we played well, especially for an end-of-season game.
"We need to improve, we know that, but today with young players in creative roles we played well.
"We can improve our killer instincts, because we need to score more goals from less chances.
"The club will not run away from the responsibility of bringing in a couple of important players to help the team immediately."
Torres' strike took him to five Premier League goals and although he has struggled to find the back of the net this season, Mourinho insists he expects him to be part of the club's future.
"Yes he's in my plans," Mourinho said of the Spanish striker. "He's a good player.
"He's not the kind of guy who will score goal after goal but the way he works and moves he contributes to the team.
"He's a player I like."
