One of your remaining decisions is choosing the foundation your new mattress will rest on top of. A foundation is a support system that goes underneath the mattress. It is designed to evenly distribute the weight of the mattress and absorb some of the compression that it sustains in normal use. A well-made foundation will prolong the life of your mattress.
Mattresses and foundations are designed to work as a unit, so it is generally recommended that they be purchased together as a set. When you purchase a mattress, the manufacturer will recommend a compatible foundation designed to support that particular mattress. And in fact, many warranties specify that a mattress must be used with the recommended foundation. But it’s still a good idea to know what’s inside your foundation, the better to understand how it will support your mattress—especially if you’re considering not using one, or using one other than the manufacturer has recommended.
The majority of foundations sold today are box springs, torsion module foundations, or slatted bases. A box spring is a wooden box with heavy coil springs that take some of the load off of your mattress. A torsion module foundation works similarly to a box spring, but instead of coil springs it has torsion bars, which are heavy wire bars typically bent at 90-degree angles.
A slatted base, also known as a built-up foundation, is made of wooden slats that span across the frame of the foundation unit. Slatted bases are (not surprisingly) firmer than box springs or torsion module foundations, and they can also be used for foam mattresses. It's important to make sure that the slats on your base are no further than 2 inches apart from each other.
For those who enjoy the comfort of today's extra-thick mattresses, but prefer getting into bed without a step-ladder or a running start, many manufacturers now also offer "low-profile" foundations for certain mattress models. A low-profile foundation is an extra-thin foundation made to accompany an extra-thick mattress so that the total height of the bed will be more in keeping with a traditional sleeping surface.
You may not want to use the box spring that is recommended with your mattress because your bedframe is European style designed for use without a box spring. Or you may wonder if you really have to spend the extra cash for a new foundation when your old one seems in perfectly good shape.
Before you decide not to purchase the foundation recommended by the manufacturer for your mattress, your first step should be to check the warranty terms. Some mattress warranties will be invalidated if a proper mattress foundation isn't used.
Next, consult the manufacturer's recommendation for supporting your mattress. Some types of mattresses, particularly foam mattresses, need the extra support a foundation supplies. Innerspring mattresses may be fine on a platform, provided the slats are not more than 2 or 3 inches apart.
Also consider that while your old box spring may look just fine on the outside, that does not mean that it is still structurally sound enough to properly support the weight of another mattress for 10 more years. And finally, consider that the cost of the foundation is generally a small percentage of the cost of the mattress. If you’ve considered all of these things and opt not to purchase a foundation, know that you’ll still need to support your mattress adequately in order to maintain its integrity over time, such as with a bed frame that is designed for use without a foundation.