My gaze naturally settled on the bed itself, which for a full-size double bed seemed huge. Hulking, even. And then—eureka!—I would have slapped my forehead if there were room: The biggest problem was the puffy, princess-and-the-pea box spring and mattress set.

“My guest bed really, really dominates the room,” I said to LeeAnn Baker, an interior designer in Seattle whom I phoned for advice. “How do I fix this problem?”

“It’s the box spring—a lot of beds don’t have them anymore, and most bed frames these days don’t need them” because they have platforms or slats to support a mattress, Ms. Baker said, adding that the most comfortable height for a bed is from 24 to 26 inches.

“My bed is currently several inches higher than that,” I said.

“Everybody lives differently in their homes,” she said diplomatically, “but you want a bed that’s easy to get in and out of. You don’t want to feel like you need a stepladder.”

These days, Ms. Baker said, most of her clients prefer a bed with a lower, sleeker profile than the inflated beds of years past. “I think the new look is a spillover from European design,” she said. “It’s become cool for furniture to go low; sofas have gotten really low, too.”

Of course, design trends come and go. But bed historians (yes, they exist) say the traditional box spring—patented in 1869 and evolving into a standard 9-inch-high wooden frame with steel coil springs—may never come back into fashion.

In fact, beds have been becoming more streamlined for centuries, said Prof. Annie Coggan, who teaches at the Pratt Institute of Art and Design in Brooklyn. Centuries ago, beds with multiple lumpy layers of straw, scratchy horsehair and suffocating feathers were considered a sign of wealth. “They were big heavy things that took two or three people to flip every day, and you had to do it everyday, because they got sweaty from people sleeping on them, and to keep critters out of the straw and hay.”

Then came the Industrial Revolution. With the invention of mass-produced metal coil springs in the 19th century, a box spring paired with “a lightweight, upholstered mattress that you can flip on your own” became the standard, Prof. Coggan said.

But no longer. Nowadays, manufacturers produce far more mattresses than box springs, according to the International Sleep Products Association. Last year, manufacturers shipped nearly 43 percent more mattresses nationwide (a total of 33.3 million) than support layers (23.3 million). Many retailers don’t even sell traditional box springs anymore.

“What made the old-fashioned box spring obsolete?” I asked Russell Jelinek, the senior director of engineering at Casper, a company that sells seven styles of mattresses but no box springs.

“Mattresses are much better than in the old days, when a box spring was necessary for comfort and support,” Mr. Jelinek said.

For mattresses, the game-changer was memory foam, a material that NASA developed to cushion astronauts’ seats. In the 1990s, mattress manufacturers began experimenting with memory foam, a high-density material that distributes body weight more evenly than steel innersprings. Fast forward to today, when sturdy hybrid mattresses—constructed with both innersprings and layers of foam—do not require another layer of springs to comfortably support a sleeper’s body, Mr. Jelinek said.

In fact, a box spring in a modern bed frame can look ridiculous. An interior designer friend of mine recently bought new beds for a project. When she tried to install box springs and mattresses, they were so tall they covered a large portion of the headboard. The box springs had to be returned.

As I talked to Mr. Jelinek (and began to imagine future houseguests thanking me for the best night of sleep they’d ever had), I clicked around on mattress websites to compare features. I discovered mattresses made with environmentally friendly recycled steel coils and all-organic materials. The brand Avocado Mattress, for instance, sells a model made with a layer of latex made from tree sap. Birch Living wraps its mattresses in all-natural wool from New Zealand sheep.

Of course, new mattress technology doesn’t come cheap—Casper’s top-of-the-line Wave Hybrid Snow model with three layers of perforated foam and a thin coating of cooling gel costs $2,995 for a full-size mattress—but maybe I could justify the expense because of all the money I’d save by not buying a box spring.

But then I noticed something else. In addition to mattresses, Casper sells a 7.5-inch-high foundation with supportive wood slats ($249 for a full-size model), described on its website as “excellent support under any Casper mattress.”

“It sounds kind of like a box spring, except with wood slats instead of steel springs,” I said. “When would you need it?”

“If you have one of those metal bed frames that doesn’t have a platform or slats for support,” Mr. Jelinek said.

Oh.

“I have one of those metal bed frames,” I said.

“Then you need a box-spring-sized foundation,” he said.

I hung up the phone and then shoehorned myself into the guest bedroom for another look with a tape measure. I realized that if I bought a 7.5-inch foundation and a new mattress, I would be able to lower the bed by 4 inches, putting me into the 24-to-26-inch zone for optimal height.

And my box spring? I’ll happily drop it off at the recycling center.