A king-size mattress measures 76-by-80-inches. Getting one up an enclosed or circular stairwell usually represents a problem, unless you can somehow bend it. Many coil or innerspring mattresses are actually hinged to bend up to 45 degrees, but there are other options.
Small Elevators or Those with Low Ceilings
If you don't live in a two-story house, you might live on an upper floor of an apartment building or condominium complex with a small elevator. Sometimes, even if the elevator is large enough, the ceiling is so low the mattress doesn't fit. If this is the case, check the stairwells. If the stairwell has an open ceiling and railings instead of solid walls, there might not be a problem. Otherwise, the delivery people must be able to fold the mattress.
Coil and Innerspring Mattresses
Depending upon the manufacturer, you can find coil or innerspring mattresses that are hinged to bend for ease of moving. One challenge is that some manufacters hinge the width, and some the length. There is generally nothing on the mattress to indicate which way it is hinged, so movers must experiment first, possibly causing damage. The degree the mattress can be bent directly relates to the type of hinge used. When buying, ask the salesperson whether the mattress is hinged and how.
Memory Foam Mattresses
Mattresses made of visco elastic foam, known on the market as memory foam, bend easily, but there are precautions to be taken. Various grades of this material makes it tricky to select the right one. The price is high and manufacturers of the lower quality product often make misleading claims that their product is the same as expensive or higher-quality products.
The natural or synthetic latex mattress is another type that can fold and is rising in popularity as a mattress core. Natural latex, made from rubber tree sap, is in the "green" family, as are cotton and wool, but doesn't pack down over time and retains it's flexible nature. It is not hot to sleep on. Another benefit is that microbial organisms and dust mites do not thrive in this material. Just as memory foam does, latex comes in different qualities, so ask whether it is natural or synthetic latex, and about quality before buying.
Whatever type of mattress you choose, lay it flat as soon as possible after moving. Do not leave it in the bent or rolled position. Don't allow low price to be the main reason for buying. Comfort is most important, since several types of mattresses bend. Try them out in the store and ask about return policies.