June 13, 2016 02:15 PM

If Selma Blair‘s turn playing Kris Kardashian on American Crime Story: The People v. O.J. Simpson had audiences wondering why they hadn’t seen more of the actress in recent years, the answer’s simple: she’s been having too much fun playing a later-in-life mom to her son Arthur Saint.

“I’ve been very much hunkered up at home,” Blair, 43, told PEOPLE while attending the 15th Annual Chrysalis Butterfly Ball, a charity event spearheaded by her close friend Rebecca Gayheart, confessing that she’s simply been loving being a mom “every day.”

“I’m up at 5:45, I’m playing Candy Land by 5:47,” she jokes. “I remind myself every moment, I think, because I did have my child later than a lot of people have children. So I’ve had a whole life to live and realize the grass isn’t always greener. I just need more sleep, but I do appreciate every moment.”

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Her son — whose father is fashion designer Jason Bleick — turns 5 in July.

“Being a single mom, at first it’s a very challenging thing,” Blair admits. “But to have that much time with him, just the two of us, has been an incredible life-changing experience. And I do not take it lightly — my gratitude.”

Lately, she’s especially been enjoying watching her adventurous son’s sense of humor develop. “He gets sarcastic, which no one should get because sarcasm isn’t great, but I have it in abundance, so I’m so grateful he’s my son,” she says.

“He gets it. He gives me lots of hugs and kisses and tells me he hopes I live a long time, even though I’m old. That’s his new thing to say before bed. We say our prayers, and then he says, ‘I hope Mommy lives a long time, even though she’s so old.’ “

Less fun for Blair is figuring out how to discipline her son. “I love him within an inch of his life, and I think sometimes you can think things are funny that aren’t,” she explains. “I hand it to moms that really know how to have a boundary early on, and that’s something really in this past year I’ve really had to be really strong about: a boundary. Because we’re buddies, we live in the same house. But no: ‘We’re not buddies. I’m your mom, and I’m here to teach you.’

“When he does something horrible but funny, it’s usually directed at me,” she adds. “So I kind of laugh, but then I realize, ‘Oh no, I can’t let him go out in the world and treat people like this!’ I’m the lightning rod for what he does. So I’ve really toned it down. He’s pretty strongly disciplined now, and it breaks my heart, but I know it’s for the best. I have to.”

Selma Blair/Instagram

After a toe-dip back to work with American Crime Story, Blair was thrilled with her experience throughout the project, and came away especially re-inspired about her craft.

“I always knew Sarah Paulson was incredible, but it’s like ‘Okay, this is what it is to love acting.’ This woman loves acting and really, really is in it. It’s hard for me to go to work. I’m tired and I have my kid on my own,” she says. “Watching Sarah Paulson is like, ‘Oh! Oh, I’ve got to get good. I only have one life to live. I better figure out how to do this.’ “

And the former Cruel Intentions star is hitting the town again, arriving at the Butterfly Ball looking elegant in a flowing black gown with purple and lavender stripes that made its way to her earlier in the day.

“It’s Christian Siriano, a dear friend of mine, and he sent this to me this morning because I didn’t have anything to wear,” Blair reveals. “I was like, ‘Help your friend out!’ And he did. He sent beautiful dresses, so I went for a gown because I think if something’s called ‘the Ball,’ you should dress up.”

— Scott Huver

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