It's rather fashionable to hide things under the mattress

Restoration Hardware's catalogs might be getting bigger, but its furniture, if you can believe it, is shrinking.

In 2012, the retailer responded to growing demand for lighter, leaner pieces by introducing a line of scaled-down furnishings. This year, its Small Spaces catalog is organized by city and residence: Los Angeles Bungalow, Boston Brownstone, etc.

It's a sharp strategy. Census data show that young people, often in search of job opportunities, are flocking to urban areas where the apartment is king.

Among the many limitations of living in a 400-square-foot studio is the lack of storage options. To accommodate, retailers are capitalizing on a piece previously relegated to children's rooms and college dorms: the storage bed.

"Storage beds have become a huge priority for us," said Janice Simonsen, a spokeswoman for IKEA USA who has worked with the company for 20 years. "We'd always had under-bed storage options like bins and whatnot, but now people want built-ins. It's cleaner, and it looks more expensive."

Beds are full of storage potential. Thanks to improved mattress technology that has eliminated the need for bulky box springs, an extra dresser's worth of space has opened up underneath. Storage beds - which typically have four or six drawers between the mattress and the floor - take advantage of it.

At IKEA, storage and daybed sales are booming, having almost doubled since 2011. The company has expanded its options from three storage beds to six, with a seventh coming in August. Its most popular line is Malm, which has two lightweight storage beds that cost between $250 and $500. One has a mattress that lifts up revealing trunk space underneath. Another, released this year, has longer legs to allow for larger drawers.

Timothy Beaver, who works in sales for IKEA's bedroom furniture department, said it's relatively new for adults to buy storage beds for themselves, rather than for children's rooms. The sales really started to spike only within the past three years, he said.

Of course, beds with built-in drawers are also a response to style trends. Under-the-bed bins are tough to pull off after college graduation, and bed skirts feel like a relic of the '90s.

As they've gotten more popular, storage beds have also become cheaper. Even though they existed 20 years ago, Simonsen points out these beds were "custom-built and terribly expensive." But as mass-market retailers such as Crate & Barrel and West Elm have started manufacturing their own versions, prices have dropped.

Pottery Barn now makes a handful of storage beds, some with interchangeable headboards, most of which cost less than $2,000. At lower-end retailers such as IKEA and Wal-Mart, beds with built-in drawers can cost as little as $120.

"I've seen a huge uptick in city clients who want small units and beautiful views," said Elizabeth Cross-Beard, an interior designer with Jenkins Baer Associates in Baltimore. "With apartments, the floor plans are pretty set, so you've got to work with what you've got."

Cross-Beard has had several clients with storage beds, particularly families. "They make cleanup so easy," she said. "You toss everything in. It takes a minute."

Although Restoration Hardware doesn't carry storage beds, Cross-Beard recommends the brand's daybeds, which have a popout trundle hidden behind a panel in the bed's base. They're a convenient option for people who don't have room for a second bed or sleeper sofa and want to invest in something that will last, she said.

Beaver points out that storage beds aren't necessarily just for those living in cramped quarters. "We have king-size storage beds," he said. "Why not utilize wasted space under your bed?"

There are other ways to save space in the bedroom if you're willing to get inventive. Designers often suggest "looking up," or considering vertical space for shelving. Some units, such as Atlantic Furniture's Captain's Bookcase children's bed or Prepac's Sonoma bed, have headboard cabinet storage that can look custom-made (with much lighter price tags). But tread lightly; if a bed has too many drawers and shelves, you'll start to feel like you're curling up in a media cabinet.

Cross-Beard says to keep it simple.

"It's true with clutter, with design and with functional furniture, less is always more."