The actress will play supermodel Jean Shrimpton in one-off BBC Four drama We'll Take Manhattan.
"I did speak to him about it," she told TV Choice. "Mainly [we talked] about what it would be like doing something different from Doctor Who, because I'd forgotten what that's like!
"He just said to really savour the experience, because it would be so different. I want to do jobs that I really care about rather than just going to work for the sake of it."
Gillan added that deciding to play Shrimpton was "a no-brainer".
"I am really interested in that period of the '60s, when the whole youth thing was so powerful, and fashion was just lovely," she explained.
"The whole feel of this drama is that it's all about the mischief that [David] Bailey and Shrimpton got up to, and I hope people will think, 'That looks really fun'."
We'll Take Manhattan marks Gillan's first role since joining Doctor Who as Amy Pond in 2010.
Her co-star Smith has appeared in a number of projects outside of the sci-fi series, including BBC Two one-off Christopher and His Kind and forthcoming Olympic drama Bert and Dickie.
It was announced last month that Gillan will exit Doctor Who alongside her on-screen husband Arthur Darvill (Rory) mid-way through the next series.
> Karen Gillan admits Jean Shrimpton role pressure
Watch a trailer for We'll Take Manhattan below: