Mattresses might not only be a safe place to stash your cash, they can also cost a pretty penny.

Sunday’s Spending Smart column highlighted some myths about buying a mattress, including the dubious coil-count specification.

Here’s some more info that didn’t fit in the column:

• Proprietary coils? Mattress makers often tout secret technology in their springs, or coils. Interesting factoid: Virtually all springs in innerspring mattresses — regardless of manufacturer — are made by one company, Leggett & Platt based in Carthage, Mo. However, the company sells many different types of springs, a spokeswoman said.
• Warehouse clubs. Some experts claim warehouse clubs have good deals on mattresses, but it might be awkward to lie on it to try it out.
• Ways to lie. Trying out a mattress is far and away the most important shopping tip. But how should you lie down? On your stomach, side, back? Quick tip: whatever position you first wake up in in the morning is probably your preferred sleeping position, says Mark Owen, vice president of brand management at mattress-maker Simmons, one of the “Big S” mattress companies along with Sealy and Serta.
• Stay offline. Because trying a mattress is so important, it’s not advisable to order one on the Internet or over the phone without personally trying the exact-same model first.
• Mattress longevity. While mattresses can last a decade, you might be more comfortable replacing yours every five to seven years, especially if you’re over age 40. Our bodies get more fussy as they age. If you sleep more comfortably at a hotel or relative’s house, it could mean you need a new mattress.
• Buy after you try. Speaking of hotels, if you’re staying at a hotel and like the mattress, peel back the sheets and note the brand and model number. Many hotels have affiliations with mattress manufacturers and can facilitate a sale.
• Mattress sales are a good deal. Blow-out sales on Presidents Day or Independence Day can feature some deep discounts, but often the low-priced advertised mattresses are usually uncomfortable, allowing a salesperson to steer you toward a pricier model.
• Don’t flip. Most new mattresses sold today have only one sleep surface and do not require flipping.
• Spending is never done. Your spending might not be over when you buy the mattress. New mattresses are thicker, with some more than 14 inches deep compared with just 7 inches. You might need new sheets with deep-pocket corners.
• Box for those springs? I found different information about whether you really need to buy a box spring along with a new mattress. Manufacturers claim the box spring, or foundation, is engineered to work with the mattress. That makes sense. But my question — if these mattresses are so great on their own, why do they need a box spring?
• Beware the delivery. There are some nasty reports of cheaper mattresses being delivered than what a customer ordered. While at the retailer, take a picture of the mattress tag with your cell phone to remind you of the model number that you bought. This prevents them from later trying a reverse switch and delivering something other than what you purchased. And always remember to pay with a credit card so you’re protected from delivery problems or phony additional charges.
• Negotiate. Especially in this economy, put on your haggle hat and negotiate with the salesperson on price.

Do you have any other mattress-shopping advice?