The 40-year-old actress - who has 23-month-old son Henry with a former boyfriend whose identity she refuses to disclose - is determined to be around for as much of her child`s youth as possible and treasures their time together because she may never have a sibling for the tot.
She said: "I`d like to haveanotherbaby but I might not, so if that was it, I want to be there for every second of it. He`s everything and I`m not going to miss any of that."
The `Good Will Hunting` actress is accompanied everywhere by Henry and says the youngster has quickly adapted to being cared for by one person, even if her career means they are often on the move.
She added to the Evening Standard newspaper: "I am a single mum, his dad`s totally in his life in Los Angeles, it`s all very amicable. But Henry goes where I go. And at the moment, I go everywhere.
"The life of a wandering gypsy is great if you`re Angelina Jolie, it`s amazing if you`ve got a plane and 20 people working for you. And actually I think it`s incredible how they do their life. But it`s just me, on my own.
"Henry has slept in chests of drawers, walk-in closets, hotel bathrooms. He`s amazing, a really funny, kind, amenable little boy."