The 'Pushing Daisies' actress – who has six-year-old daughter Gracie with former partner David Thewlis – has been dating the Welsh actor for nine months.
She said: "I really want more children. Gracie is my little mate as well as my daughter. And she's so caring and loving. I always tell her, 'You're my angel from heaven.' I'm big on manners so she can't have anything without saying please or thank you.
"I love being a mummy and I'm a good one."
However, Anna, 35, is unsure whether she will find it easy to conceive as she was warned before having Gracie she may have difficulties getting pregnant.
She told Marie Claire magazine: "It was a total surprise, doctors had said it would be difficult to get pregnant because I had endometriosis. Well, it wasn't. One time we were a bit naughty and then I became pregnant.
"Whether that will happen as easily again, I don't know. Things could be different now I'm older."
Anna admits her relationship with Rhys – who previously dated Sienna Miller - is "very, very serious" and she is always thinking about the future with him.
She said: "Of course I do [still think about forever]. With Rhys, certainly, things are very, very serious.
"But because we've been through so much, it's not been that frivolous 'woo-hoo' type of love. We've had to be really adult about things.
"Rhys has never been in a position where he's had to take on somebody else's child. That isn't for everybody."