A product of City's academy, Trafford kept 29 clean sheets in 45 Championship matches for Burnley last season before rejoining the Premier League champions in July.
He started their opening three league games but was then restricted mostly to FA Cup and League Cup appearances following Italy goalkeeper Donnarumma's deadline‑day signing.
"It has obviously been very up and down throughout the season because I haven't played too much and obviously I had a decision to make in the summer," Trafford told BBC Sport.
"Everyone always thinks when you make decisions (for) the best possible outcome and obviously it hasn't been the best possible outcome, but I have just tried to either improve every day and just try and stay positive, try and stay happy."
Despite limited opportunities at City, Trafford made his England debut in March in a friendly against Uruguay and hopes to be included in Thomas Tuchel's squad for the World Cup.
"Obviously I want to try and make the squad. It will be a great experience for me. It will be brilliant, but I can't do anything between now and then," he added.
City face Southampton in the FA Cup semi-finals on Saturday.