03/22/2012 at 10:25 AM EDT
About seven weeks after the birth of her son
, Xander, January Jones
was back to work in the role that made her both admired and pitied, the former Betty Draper, now the re-married Betty Francis, on AMC's Mad Men
With her baby still "really little," says the actress, 34, returning to the set
"was tough with the long days. But work made it really comfortable for me."
As it was, "Every season I have a little kind of first day of school nerves. The first episode I'm always finding my way back into my character's shoes. … But then after a few days, I'm able to fall pretty easily back into her, and find her voice and her body language and everything that I do for her," says Jones.
"I also found it helpful to be that far along in my pregnancy
, just because I was on such a roller coaster of emotions. I found it really therapeutic to go to work and to be able to channel all these mood swings into Betty. It was really great, actually.
Besides behavioral shifts, there is something else the '60s suburban housewife is known for: her fetching fashion style.
"We didn't do anything specifically for me because of my post-baby [body]," says Jones, "but Betty's had style evolution."
Besides adapting to the passing of time, the changes also had to do with the character's new marriage.
"I think especially since she's been married to Henry Francis and has become a politician's wife, she's made a change in her look," says Jones. Costume designer Janie Bryant "consciously made a decision to change her silhouette. Betty likes to play dress up, so instead of molding herself after a Grace Kelly or a movie star, she's wearing things that she thinks a Jackie Kennedy would wear."
That means "instead of the petticoats and the big skirts, she's wearing the little suits. And her attire for the bedroom has always been sort of ridiculous, those big gowns and things."
's season 5
kicks off with a special two-hour episode Sunday.
Reporting by CATHERINE KAST