Plush or firm? There is no right or wrong answer. You might've always believed that you like a firm bed until you try a softer one, or vice versa. So try them all and choose the mattress that offers you the most comfort.

Whether you sleep on your back, side or stomach, the correct mattress should be comfortable for your whole body and keep your spine in alignment.

Sleeping posture is one of the most important considerations. Choose a mattress that allows your hips and shoulders to sink slightly while still supporting your waist, to make sure it keeps your spine straight.

If you have difficulty rolling over, the bed is probably too soft. If the bed is too firm, you'll feel pressure against your hips and shoulders. Lie on your back and try to slide your hand under the small of your back. If your hand slides in too easily, the mattress may be too firm.

If you're heavier, you'll need more support to keep your body aligned. So make sure that the mattress you choose will keep your spine perfectly aligned the whole night through.

By spending five minutes each on your back and both sides (as well as your stomach, if that's one of your normal sleeping positions), you should have enough time to determine if the mattress is the right choice for you. If you sleep with a partner, try it out together.

The general rule of thumb is to buy the biggest bed you can fit into your room. The larger the bed, the more room you (and your sleeping partner) have to move during the night without disturbing each other.

Taller people need more room to stretch out comfortably, so it's important to check that the mattress is longer than the tallest sleeper.