You’ll spend a third of your life on a mattress, which means picking the right one is important. Start with your preferred sleeping position and how much support you need. Here are a few tips.

Should you buy a firm or soft mattress? Generally, heavier people and back or stomach sleepers will do better with firmer mattresses, while lighter people and side sleepers enjoy softer mattresses. Temperature is also an issue: Softer mattresses sleep warmer since your body is sinking into a layer of fabric and foam. Keep in mind that all mattresses have a break-in period, and the way the mattress feels on your first night won’t be how it feels after a week or two.

Do you want a hybrid or foam mattress? The next big question is whether you want a foam mattress or a hybrid model that layers foam with built-in springs. We tend to recommend hybrids because they are more stable and supportive, and they usually stay cooler. Hybrids are often slightly pricier. Foam mattresses tend to be softer, lighter, and cheaper.

What size mattress do you need? The prices below are based on the queen size, but almost all mattresses come in the standard sizes of Twin, Twin XL, Full, Queen, King, and California King. You’ll want to buy a mattress based on the size of your bed frame.

How easy is it to set up a bed-in-a-box? Most of these mattresses are delivered in a box, vacuum-sealed, and rolled up. Some are pretty heavy—up to 150 pounds—so be sure you have someone to help you. After you unroll your bed-in-a-box mattress and cut the vacuum bag open, it’ll immediately begin to inflate, so unbox it on your bed frame or near it. We have a helpful guide on how to set up the mattress you bought online with more tips. The mattresses are usually ready to go in a few hours, but most manufacturers recommend giving them two days to reach their normal state.

Should you wait for a sale to buy a mattress? Mattresses go on sale often. If you see one at full price, there’s a strong chance you can save hundreds of dollars by waiting for the next big sale event (every few months).

What if you don’t like the mattress you bought online? Most of the mattresses we have tested and recommend have at least a 100-night testing period and a 10-year warranty. You may want to look at the company’s policy as you may be on the hook for a nominal return fee.