One of the most common causes of persistent lower back pain is a mattress that’s either too soft (allowing hips to sink, creating a “V” shape) or too firm (creating pressure points at hips and shoulders that force the spine to twist). Here’s the evidence-based guide.
The Firmness Sweet Spot
A landmark study in Lancet found that medium-firm mattresses produced significantly better outcomes for chronic low back pain than firm mattresses — contrary to the old advice to “sleep on a hard mattress.” For most people, medium-firm (5-7 on a 10-point scale) is optimal.
What to Look For by Sleep Position
Side sleepers: Need slightly softer to allow hip and shoulder contouring (medium, not medium-firm). A mattress that’s too firm will create lateral curvature in the spine.
Back sleepers: Medium-firm works well, providing lumbar support without flattening the natural curve.
Stomach sleepers: Firmer is better to prevent hip sinkage that hyperextends the lower back — though sleeping on your stomach is generally not recommended for back pain.
Memory Foam vs. Innerspring vs. Hybrid
Memory foam contours well but can sleep hot and may be too soft for heavier individuals. Innerspring provides good support but less contouring. Hybrids (coil base + foam top) give most people the best combination of support and pressure relief, and are what most PTs recommend for back pain.
When to Replace Your Mattress
If your mattress is more than 8-10 years old, shows visible sagging, or if you wake with more pain than you went to sleep with — it’s time. Even a high-quality mattress loses its support properties after a decade of use.
Interim Solution: Mattress Toppers
If replacement isn’t immediately possible, a 2-3 inch medium-firm memory foam topper can significantly improve a mattress that’s too firm. It won’t fix a sagging mattress, but it can add needed contouring to an overly rigid surface.