As long as you're consistent and don't use both spellings in a single document, you'll be fine. Final point: whichever spelling you favour, it's a single word. Don't write 'strait jacket' or 'straight jacket'.

Is it straight jacket or straight jacket?

Although straitjacket is the most common spelling, strait-jacket is also frequent. Straitjackets are also called camisoles. The effect of a straitjacket as a restraint makes it of special interest in escapology.

How do you spell straight like a straight line?

Straight is always an adverb, whereas strait is a noun

As an adjective, "straight" has several meanings, including level, upright, not bent, extending in the same direction, accurate, and honest. As an adverb, "straight" means directly or in a "straight" line. The noun "strait" usually refers to a narrow waterway.