Hailee Steinfeld's clearly having an impact in her role as Queen of Buffalo -- Christian Benford tells TMZ Sports she's made the Bills' best player, Josh Allen, a "happier" man!!

We caught up with Buffalo's star cornerback on Friday -- and with Steinfeld dominating the box offices with her new "Sinners" flick, we had to ask how her two-year-long relationship with Allen has impacted his quarterback.

Benford told us he's noticed a much more jovial signal-caller -- explaining, "You could say he's happier. You know what I'm saying?"

"Go home to a woman that he loves -- a woman that he's happy with."

As for her new vampire-themed movie with Michael B. Jordan, Benford praised her work there, too.

"It was cool," he said. "It was actually a great movie ... I really enjoyed it."

Benford's got a lot of reasons to smile just like Allen these days -- after all, he just inked a massive, $69 million contract extension to stay with the Bills -- but he told us he hasn't gone crazy with his credit card just yet.

In fact, he said he doesn't have many plans to ever bust out his wallet in extravagant fashion -- explaining he's preferring to save his cash as well as invest it into real estate properties.

Benford's also recently been busy writing -- he authored a children's book titled, "Stylish Safari: The Adventures of Being You," and the message is awesome.