Cox, 45, underwent in-vitro fertilisation to become a first-time mum at 39, and Arquette admits he's ready to expand the couple's family again.
But the 38-year-old dad confesses he doesn't have the energy to make regular appointments to see fertility specialists and have sex.
He says, "It takes a lot for us to do it (have a baby), so maybe adoption. Listen, I like practising as much as possible! But it's hard... I'm exhausted!"