Foundation

When two sleepers keep drifting toward each other, the surface between them has usually developed a slope. A weight difference can contribute, but it's rarely the whole story — the direction of the roll is a clue worth reading.

Height charts assume a fixed surface — but your mattress isn't fixed. A plush bed lets your shoulder sink and shrinks the gap a pillow needs to fill; a firmer bed keeps you higher. The right height is set by both, not by sleep position alone.

Plywood is a reasonable fix for a foundation problem — wide slat gaps, a flexing frame, a sagging box spring. It won't restore a mattress that's lost support in its own core. Check the warranty terms before adding anything underneath.

There's no single correct number — the spacing your mattress needs is set by its manufacturer, and some warranties name it as a condition. What matters more: a foundation that doesn't hold the mattress evenly can mimic a worn-out core.

A mattress losing support in the middle and a mattress sitting on a failing base can feel identical from where you're lying — because the mattress follows whatever shape is underneath. Guessing wrong means paying for the fix that wasn't the problem.