Denise Fergus said she and the two-year-old's father, Ralph Bulger, hit "rock bottom" as their son's third birthday approached, shortly after he was abducted from Bootle Strand shopping centre in Liverpool and killed in February 1993.
In an extract from her forthcoming memoirs, I Let Him Go, serialised in the Mail on Sunday, Ms Fergus said: "I think we both hit rock bottom, I certainly felt I had nowhere left to fall.
"Did I try to kill myself? Not quite. Did I think about killing myself? Absolutely. Very often in great detail."
Ms Fergus said their grief was compounded by her feeling that Mr Bulger blamed her for momentarily letting go of James's hand while at the shopping centre, clearing the way for child killers Jon Venables and Robert Thompson to swoop and commit atrocities that would send shockwaves across the country.
Venables and Thompson, who were just 10 at the time of the killing, were jailed for life but released on licence with new identities in 2001.
In her memoirs, Ms Fergus described her horror at the behaviour of the defendants' families during their murder trial.
She said: "Imagine my surprise when I saw smiles and laughter coming from their supporters as they interacted with Thompson and Venables in the dock. I just couldn't believe my eyes.
"Then I saw their shoulders start shaking and I thought, finally, some tears, but as I looked closer I saw they were laughing at something that had been said to them.
"I have no idea if they knew who I was, but that image of them is burned on my memory and will be with me until my dying day.
"My son was dead and they were chuckling without a care in the world."
She added that she had not gone shopping alone since James was snatched, almost a quarter of a century ago.
Earlier this month, Venables was charged over indecent images of children for a second time.