Life at Stamford Bridge has got off to quite the start for the 26-year-old, who has already netted 10 goals for the west Londoners despite battling hamstring and groin issues.
Those complaints led to Costa missing Spain's international fixtures this past fortnight, with that break allowing the former Atletico Madrid striker to make what Mourinho says is a full recovery.
It is a timely boost ahead of Chelsea's run of eight matches in 24 days - the start of what Mourinho calls a "beautiful" period, albeit one which will be a culture shock to Premier League new boy Costa.
"I believe [this period has set him up for the rest of the season], but now we are going to have a period that is new for him," the Blues manager said of the striker, who is one yellow card away from suspension.
"I always think that the Christmas period for players doing it for the first time in their careers is more difficult.
"The English players, or those who have been here for many, many years, are more physically and, especially, more mentally adapted and prepared to cope with that incredible marathon of football we have to face.
"But in these two weeks he has had a little bit of a holiday, but one spent with a Chelsea physio
Even in that small period of holiday he was working many, many hours per day with our physio.
"After that he came back, he keeps going in the right direction and, at this moment, we feel he's free of his old injury."
Intelligent management over the festive period will be key to preventing any further issues arising for Costa, who Mourinho admits he has already sat down with to talk through what to expect in the coming weeks and months.
"We spoke yesterday about it," the Portuguese said
"But we go match after match.
"Diego has four yellow cards
Am I going to protect him for any game? No way
He plays, when he gets the fifth he gets the fifth because the important game is against West Brom.
"After West Brom is Sunderland
I am not thinking about Newcastle, Tottenham or Stoke - for us it is the next match.
"With Diego, we have to go match by match, but the way he trains and expresses himself in training, he has a free mind
He's free of fears, at this moment
He is good."
A fully-fit Costa is a worrying prospect for Chelsea's Premier League rivals and, in particular, Saturday's opponents West Brom.
It is a match the west Londoners head into atop of the standings having accrued 29 points from the first 11 matches - a start only bettered twice in Premier League history.
Such fine form had even led one bookmaker to pay out on the Blues winning the title, although Mourinho scoffed at the suggestion that the title race was all but over.
"No complacency, that's for sure," Mourinho said
"If we lose matches, and I believe we will, it won't be because of complacency
It will be because football is football.
"It was not in the Premier League but I can give you an example: our game against Maribor
We lost two points, but it wasn't down to complacency
It was because of football.
"Their goalkeeper was the man of the match and we missed so many chances
My team played tremendously well in the second half but we still lost two points.
"You lose points because it's football, because the opponents are better than you, but not because of complacency."
Source : PA