Which bed base for a pocket-sprung mattress: slats, divans and the 7 cm rule

A mattress sits on something, and that something decides how it feels and how long it lasts more than most people realise. A good mattress on a bad base dips in a year, and the guarantee will not cover it. Here are the bases, what each does, and the two rules.

The two rules

1. Slats no more than 7 cm apart (some makers say 6 cm, a few allow 7.5). Wider gaps let the mattress sag between the slats and the springs push into the gaps. Every guarantee has a version of this rule.
2. A centre support on a king or super king: a rail down the middle with at least one leg to the floor. Without it the base flexes in the middle and the mattress follows.

Check both before a new mattress arrives, not after.

The bases

Sprung divan. A fabric-covered box with its own layer of springs on top. The most forgiving base: it adds a little give, softens the overall feel slightly, and spreads the load across the mattress. The traditional pairing for a pocket-sprung mattress and the one most guarantees assume. Two-piece in king sizes so it goes up stairs. Takes drawers. Not pretty.

Platform-top divan. The same box with a firm, flat top instead of springs. Firmer overall feel than a sprung divan, very supportive, the best base for a heavier sleeper or anyone who finds their mattress too soft. Also takes drawers.

Slatted frame. Wood or metal frame with slats. Looks better, lighter, easier to move. Two kinds:

• Rigid slats (flat, fixed): supportive, feel like a platform top, fine if the gaps are under 7 cm.
• Sprung slats (curved beech that flexes): adds give, feels softer, and can let a heavy mattress or heavy sleeper sag if the slats are thin or widely spaced. Fine with a good mattress and close spacing; check the frame's stated weight.

Cheap frames fail on slat spacing, thin centre rails and slats that pop out. A frame is only as good as its slats.

Ottoman (storage) bed. A frame whose base lifts on gas struts to reveal storage. The base is a solid or slatted platform, so it feels firm and flat. Check the slat gaps when it is closed, and check that a deep mattress does not make it too heavy to lift.

Bunk and cabin beds. A slatted or solid platform with a maximum mattress depth marked; use it.

Adjustable beds. The base bends; the mattress has to bend with it. Pocket-sprung mattresses with a steel edge do not. Foam, foam-core and some specifically flexible pocket-sprung mattresses do. Check compatibility with the base maker before buying either.

The floor. Fine for a night or two. Longer, a mattress on the floor cannot breathe underneath and can develop damp and mould on the base.

What the base does to the feel

If a mattress feels too firm, the base is worth checking before buying a topper: moving from a platform to a sprung divan or sprung slats softens it noticeably. If it feels too soft or saggy, the reverse.

Old bases

A divan that has done fifteen years has springs that have gone and a top that has hollowed. Put a new mattress on it and the hollow comes through within months. If the base is older than the mattress it is replacing, replace it too. A new mattress on an old base is the most common guarantee dispute there is, and the maker will ask.

How we specify it

Every Chapter guarantee assumes a suitable base: a sprung or platform-top divan, or slats no more than 7 cm apart with a centre rail on king and super king. The New Parent, with its foam core, suits a platform top well; The Hot Flush prefers slats or a sprung divan so its vented border can breathe; the Hotel Bed is heavy and wants a frame that does not flex. Each product page says which.

The short version

• Slats no more than 7 cm apart; a centre rail on kings. Check before delivery.
• Sprung divan softens, platform firms; slats in between depending on type.
• Adjustable beds need a mattress that bends.
• Replace a base older than the mattress it carries.