"straight posture" is a correct and usable phrase in written English.
You can use it to describe the physical position of someone or something. For example: "She stood with a straight posture, ready to begin the challenging project."
The elegance of her straight posture denied her failed joints from a rheumatic youth.
On the conductor's podium Mr. Jurowski cuts a dashing figure with the uncompromising straight posture of a ballet master.
With her straight posture and impeccable makeup and long blond hair, she betrays little of the strain she has endured.
His niece has a more composed air about her, helped by her impeccably straight posture, and lean, 6ft figure endowed with incredible legs.
While studying at a monastery in Santos, Brazil, she noticed the straight posture of the Brazilian Indians, who stood in the sand with their heels lower than their toes.
Ms. Foote's Alberta is still a beauty, even when her face goes empty with resigned hopelessness, and her exquisitely straight posture still exhales an air of good breeding and aristocratic entitlement.
Vegas has ramrod-straight posture, which makes him look taller than his 6 feet 2 inches.
He was older, leather-skinned and square-jawed; he wore a baseball cap with the insignia and number of an army airborne division, and had the ramrod-straight posture and straight-spoken demeanor to match.
"In the mind of the public, we literally go overnight from being an object of desire to being discardable," observes Legato, a slim and elegantly dressed 68-year-old with a perfectly coifed grayish-blond pageboy and ramrod-straight posture.
When she speaks of her son's battle wounds or the numbers of men he has killed, she emanates a sexual thrill even as she maintains her soldier-straight posture.
Guided by a young man in tuxedo pants with stick-straight posture, two dozen mostly amateur dancers navigated their way through the public passageway between West 55th and 56th Streets in Manhattan on Saturday like so many cabbies trying to muscle through Times Square at rush hour.
