The Rock is exactly what it sounds like: an extra-firm innerspring with a moisture-wicking quilted top and almost no soft layers between you and the coils. If 'firm' beds always feel too soft to you, this is the one. Most-recommended in our showroom for stomach sleepers and people with severe lower-back pain.
9/10 on our firmness scale. Almost no contour — your spine stays absolutely straight.
Quilted fabric pulls sweat away from skin overnight.
Reinforced edge support and high-gauge coils. Holds heavier sleepers without sagging.
Most extra-firm beds at this price are foundation-grade. This one's a real mattress.
A 9/10 firmness — supportive top with minimal contour. Best for back and stomach sleepers, plus heavier sleepers who want less hug.
Built for adaptive support and breathability. Every layer is hand-checked before it ships from our warehouse.
Diamond Mattress is a 4th-generation family-owned company that has been handcrafting mattresses in Southern California since 1946. Founded by the Pennington family in Compton, California (now headquartered in Rancho Dominguez), Diamond is one of the few mattress manufacturers in America that is fully vertically integrated. They make their own pocketed coils, process their own memory foams, and cut and sew their own fabrics — all under one roof. This level of control over every component means Diamond can maintain strict quality standards that outsourced manufacturers cannot match. Every Diamond mattress is CertiPUR-US certified, GREENGUARD Gold certified for low chemical emissions, OEKO-TEX tested for harmful substances, and ECO INSTITUT certified for environmental safety. Diamond also uses REPREVE recycled fibers in select products, demonstrating their commitment to sustainable manufacturing practices.
The Diamond Rock Extra Firm 12" Mattress is built in Diamond’s Southern California factory using their proprietary manufacturing processes. Diamond is one of the few mattress companies that makes their own pocketed coils, processes their own memory foams, and sews their own fabrics in-house. This vertical integration gives them direct control over every component and the ability to innovate faster than brands that rely on third-party suppliers. The mattress features CertiPUR-US certified foams, ensuring they meet strict standards for content, emissions, and durability. GREENGUARD Gold certification confirms low chemical emissions for a healthier indoor environment.
The firm comfort level is designed for back sleepers and stomach sleepers who need a flat, supportive surface that prevents the hips from sinking below neutral alignment. Heavier sleepers (200+ lbs) often prefer firm mattresses because they maintain support under greater body weight without excessive compression. The firm surface also tends to sleep cooler because there is less foam material trapping heat around the body.
As an authorized Diamond dealer, LA Mattress Store carries the complete Diamond lineup in all five of our Los Angeles showrooms — Glendale, West LA, Hancock Park, Koreatown, and Studio City. Walk in any time during business hours to try this mattress in person. Our sleep consultants can help you compare firmness levels, construction types, and find the right mattress for your sleep style and budget. Every purchase includes free White Glove delivery anywhere in the Los Angeles metro area — our team delivers to your room of choice, sets up the new mattress, and removes your old one at no extra cost. Same-day delivery is often available. Diamond offers a 120-night comfort exchange (exchange for a different model if needed) and a 20-year manufacturer warranty — one of the longest in the industry. LA Mattress Store coordinates all warranty claims on your behalf. We also offer 0% APR financing for qualified buyers, making it easy to invest in better sleep without paying the full amount upfront.
Diamond Rock Extra Firm 12" Mattress is available in Queen, King, CA King, Twin, Twin XL, Full. Queen starts at $799. All sizes include free White Glove delivery in Los Angeles.
Have questions? Call us at (800) 218-3578 or visit any of our 5 Los Angeles showrooms to try it in person.
