You spend about a third of your life sleeping, so the mattress size you choose to sleep on should be comfortable and support your health and well-being. Mattresses come in twin, twin XL, full (or double), queen, king or California King sizes.

Several factors can influence what size of mattress you buy. Here are some tips to help.

Consider the sleeper. The most important factor to consider is you! You need to select a mattress that will accommodate your height and size, as well as any partners or pets.

The average healthy person moves 13 times an hour while sleeping and can make multiple full-body turns a night. If you are tired and sleep-deprived, you might move less, but you should plan for healthy sleep. For sound sleep, you need freedom of motion – and that means you need space!

It is typically recommended that if you are sleeping with a partner, that you buy at least a queen-sized mattress, instead of a full or double sized mattress.

Do the math – look at your height and width – as well as any sleeping partner. A typical full-sized mattress is 54 inches wide and 75 inches tall. For a single sleeper, that is 54 inches of sleep space (15 inches compared to a Twin or Twin XL mattress). If a sleeper is six feet tall, a full-size mattress offers 3 inches of additional space when the sleeper is fully extended. Couples or families who co-sleep with children may find queen, king, or California king size mattresses more accommodating.

Next, consider the size of the room where the mattress will go and where you might place your bed.  There can be small variations in sizing between manufacturers, so it’s important to check with the manufacturer for the exact measurements if it might be a tight fit.

Maneuverability is also a factor to consider. Will the mattress need to come up a flight of stairs or through a narrow hallway with a turn? Many shipped mattresses now are compressed and will expand when opened. For apartment dwellers with narrow stairwells, this has made it possible to get a larger mattress into a tight space more easily.

Also consider what else is needed for the mattress size you select. Do you have a bed frame that will accommodate the mattress size? A foundation is a wood or metal bed base that sometimes includes slats lying across the top. This is sometimes covered in fabric. The slats are spaced apart to provide air circulation and add strong structural support. A foundation makes for a durable, protective base for your mattress. Determine if you need to buy a mattress foundation and follow manufacturer directions. You will need linens for the mattress too.

Here are a few more tips to help you shop for a mattress:

Try out different mattresses in person. Go mattress shopping in person. Check mattress size. Wear comfortable clothes and shoes you can easily slip off so you can lie down. Compare a variety of support levels and styles within your budget. Finding a bed that “feels” right is a personal choice. If you will have a sleeping partner, bring them along.

Be sure the mattress contains certified foam. A growing number of consumers want to be sure the flexible polyurethane foam used in their bedding (and upholstered furniture, too) is CertiPUR-US^® certified. Certified foam is your assurance that the foam in your mattress meets rigorous standards for content, emissions and durability and is analyzed by independent, accredited testing laboratories. Certified foams are screened for relevant chemicals, including flame retardants, that are classified as carcinogens, mutagens or reproductive toxins and are harmful to human health. Certified foams are made without formaldehyde; ozone depleters; mercury, lead and other heavy metals; or phthalates regulated by the U.S. Consumer Product Safety Commission. It also means the foam has low VOC (volatile organic compound) emissions for indoor air quality (less than 0.5 parts per million). Check the CertiPUR-US directory of participating companies and brands offering pillows, mattresses and upholstered furniture using certified foam before you make a purchase.

Find a reputable dealer. Furniture stores, department stores and sleep specialty shops all sell mattresses. Ask friends and family for referrals. If you don’t feel a salesperson is knowledgeable or helpful, take your business elsewhere.

Do your research. Do research online about the mattress you are interested in and read reviews, paying attention to mattress size. Ask the salesperson to show you illustrated or actual “cutaways” of the interior of the different mattresses and foundations. The mechanics of innersprings and foams vary widely, which can greatly affect comfort.

If buying online, check customer service out before you purchase. If you choose to buy a mattress online, you won’t have the opportunity to try it out before it arrives at your home, so read the reviews and carefully check return and shipping policies. Be certain there is good customer support in place. An easy test you can do before ordering is to call customer support and talk with the representative. Find out how easy it is to make a return if you need to make a change.

Think long-term. Go for the best value, not the lowest price. To ensure long-term performance, buy the highest-quality mattress you can afford. View it as a 7- to 10-year investment in your health and well-being.

For more information about mattress shopping (and advice on how to get a better night’s sleep), visit the Better Sleep Council.