Kim Kardashian and Kanye West arrive at the 2016 MTV Video Music Awards in New York. Picture: AP

The couple – who have children North, four, and Saint, 18 months, together – found a surrogate to carry their third child because the 'Keeping Up With the Kardashians' star has been warned off getting pregnant again by doctors but it was the rapper who was keen to move the process forward.

An insider said: "Kim was never going to let herself get pregnant again. It's just too dangerous for her. Kanye was initially the one pushing for baby No. 3."

And the 40-year-old rapper and his 36-year-old wife are ready to welcome another child into their family because they're in a "great" place in their marriage.

READ: Kimye 'hires' surrogate for baby #3

The source added to PEOPLE: "They are both very excited to give their kids a sibling. Things are great between them. They act very happy together."

My baby girl turned 4 years old today! She's my light & my everything!!! I love you to the moon & back North

A post shared by Kim Kardashian West (@kimkardashian) on

The surrogate has already been found through an agency, and it's believed the couple are willing to pay the unnamed woman $45,000 in 10 equal instalments, though if it is a multiple pregnancy she will receive an additional $5,000 per child.

In addition, if the surrogate loses reproductive organs in the process, she receives an additional $4,000.

They're are also required to deposit $68,850 with the agency.

In return, the surrogate must refrain from smoking, drinking and drugs during the pregnancy, and she cannot go in hot tubs or saunas, handle or change cat litter, apply hair dye, drink more than one caffeinated drink per day or eat raw fish.

She has also agreed to restrict sexual activity in the weeks leading up to getting pregnant including foregoing intercourse for three weeks after embryo implantation.

The agreement also states the 40-year-old rapper and his 36-year-old wife "assume the legal and parental responsibilities for any child ... that may possess any congenital or other abnormalities or defects."