When you have a good idea, it’s generally good advice to sleep on it. But Gregg Richard, CEO of P.C. Richard & Son, slept on one big idea for three years before rolling it out. Now other people are sleeping on it.

While the more-than-a-century-old independent chain based in Farmingdale routinely adds products, it a year ago almost to the day began selling mattresses at a few stores.

The firm will have mattresses in 56 of its 66 stores (including a dozen of 19 Long Island locations) within a week and anticipates mattress “galleries” in all its stores within two months.

“We felt we were sending our customers to our competitors, because we weren’t giving them the choice,” Gregg Richard said. “Now that they have a choice, they’ve proven to us that we were right. They’d rather buy from us.”

The firm is rolling out the mattresses more rapidly than planned, because Richard said the category has been “successful beyond my wildest dreams.”

“Because of the success last year, it was an all-out team effort to get these open as quick as humanly possible,” he said.

It might be an irony that mattresses are proving a way to wake up sales, which weakened in some categories. Customers still flock to P.C. Richard & Son for refrigerators, stoves, ovens and appliances, but some buy electronics, well, electronically.

“The electronics business isn’t what it used to be,” Richard said. “The computer, home-office category hasn’t been terrific, but we’re still doing fairly well. If our customers want something, we’ll be there to sell it to them.”

While to an outsider, selling mattresses may seem a departure, some bed frames and mattresses involve technology. And when people buy houses, they often need refrigerators, TVs and a place to sleep.

The firm, which says it’s “changing the way you buy a mattress,” sells Sealy Posturepedic, Stearns & Foster, Optimum and Tempur-Pedic as well as other brands.

“The most difficult part of the mattress business is operational,” Richard continued. “You need showrooms. We have them. You need great salespeople. We have them. You need advertising. We have it. You need a warehouse. You need trucking, home delivery, drivers and helpers. We have it. And we have the loyal customers.”

Other appliance and electronics retailers already went into the bedding business, such as Conn’s HomePlus, RC Willey, ABT, ABC Warehouse and BrandsMart USA.

“I talked to these guys. They said it’s a good business,” Richard continued. “I’m friendly with most of them. I kept pushing it off.”

The firm got requests for mattresses on customer cards filled out in stores. Then it tested the concept, tucking mattress “galleries” in the back of seven Connecticut stores a year ago. Mattress galleries sprouted in spaces used for stockrooms, rather than displacing items.

“We were able to break through the walls and make the stores a little bigger,” he said. “It required a lot of capital to get in the business. It forced us to look at every store. And when we went in to do the mattress galleries, we gave many stores a facelift.”

The company, which paid for renovations out of funds from operations, sells 20 different mattresses in its 10,000-square-foot Rego Park, Queens store and 35 in the 50,000-square-foot Riverhead store.

“Each store is different,” he said. “We have enough of a section, so our customers can make an educated decision.”

The retailer offers mattresses and bedframes ranging from under $200 to $10,000. Some frames offer massages, go up and down and include USB ports, phone plugs and chargers.

Although the firm says it will match others’ prices, it provides information about the product, including how it’s built, hand stitching, foam and oils. But comfort is king.

“It’s what you’re comfortable on, what you’re used to sleeping on,” Richard said.

He assumed customers would want to test mattresses, but he’s finding many choose convenience, buying online.

“I thought people would educate themselves, come into the store,” he said. “The business we do online without people ever lying on a mattress is amazing.”

Although some customers are surprised to see P.C. Richard’s softer side, Richard says his firm evolved, initially selling hardware, adding appliances in 1909 and by the 1930s and 1940s selling TVs.

“We started as a hardware store. We don’t sell hardware anymore,” Richard said. “We’ve changed our business model many times. Microwaves used to be a gigantic part of our business. VCRs. That turned into DVD players. CD players were big. It changed to the iPod and Wi-Fi.”

Executives have moved back and forth between appliance and electronics and mattress retail, bridging the two businesses. The former CEO of Bosch Appliances is president of Serta and a former Whirlpool executive is a top executive at Sealy Posturepedic.

“Lots of customers come in to buy a mattress and wind up buying something else too,” he said. “Maybe they buy a TV. It’s the advantage we have. We have lots of categories.”

P.C. Richard delivers on its promises, charging $49 for delivery, set-up and disposal of old mattresses, although it periodically offers free delivery.

And it’s expanding into the fitness business, selling Fitbits and trackers that measure steps, heart rate and calories, as well as home security and automation equipment, including smart thermostats and devices that use phones to unlock doors.

It sells home-office desks and some furniture used with TVs, but don’t expect the chain to turn into a furniture store.

“We’re not at this point selling dining room sets or couches,” Richard said. “We’re not looking to expand deep into home furnishings.”

The store expanded its slogan from the “appliance, TV, electronics giant” to “the appliance, TV, electronics, mattress giant.”

“The mattress business is very similar to our business,” Richard said. “The peak times are really the same holidays.”

The store competes with specialty retailers such as Bethpage-based Sleepy’s and department stores, but Richard believes his firm is simply expanding its niche.

“I’ve been competing with people for 105 years,” Richard said. “Most of them aren’t here. Competition isn’t new to us.”

There is a risk that a customer unhappy with a mattress could be turned off to the store and that online orders could be cancelled. But Richard isn’t losing sleep over possible problems, as the firm finds money hidden under mattresses.

“We’re in business to make customers,” Richard said. “We’re not in business to try to make an extra-quick buck for the short term.”