The Red Devils have already exceeded last season's Premier League points total of 69 this term, having amassed 71 with six games remaining.
However, Man United look set to finish a distant second behind Man City, while their shock Champions League exit at the hands of Sevilla in the last 16 highlights room for improvement.
Mourinho, who has spent in excess of £300m since taking over at Old Trafford, insists that the club will not be irresponsible in the market.
"We are not going to spend more than we can. We are not going to do anything crazy," the Portuguese told Sky Sports News. "We are just trying to improve a little bit more. That's what we are going to try.
"Everybody will try to improve - like we did from last season. Last season we finished sixth and this season we are going to finish, hopefully, second.
"Next season, we are going to try to improve, but let's see what happens. Maybe also City will invest massively and they don't let the others close the gap to them, I don't know.
"But it is not about us and them, it is about us and them and Liverpool and Arsenal and Chelsea and Spurs. It is not City and United. It is about the six."
Man United are in action on Sunday as they host Premier League basement side West Bromwich Albion.