The Zinus 12 Inch Gel-Infused Green Tea Memory Foam Mattress is a top choice for those looking for a firm and supportive mattress on Amazon. This mattress is constructed with multiple layers of foam, including a top layer of gel-infused memory foam that helps to regulate temperature and provide pressure relief. The green tea infused into the foam also helps to keep the mattress fresh and odor-free. With a king size option available, this mattress is perfect for those who need a little extra space and support while they sleep.1. Zinus 12 Inch Gel-Infused Green Tea Memory Foam Mattress | Firm Support | King
The Classic Brands Cool Gel 2.0 Ultimate Gel Memory Foam 14-Inch Mattress is another top contender for the best firm king mattress on Amazon. This mattress features a top layer of gel-infused memory foam that helps to dissipate body heat and keep you cool throughout the night. The high-density foam layers provide excellent support and help to alleviate pressure points. Plus, the mattress is hypoallergenic and resistant to dust mites, making it a great choice for those with allergies or asthma.2. Classic Brands Cool Gel 2.0 Ultimate Gel Memory Foam 14-Inch Mattress | Firm Support | King
The Tuft & Needle Original Mattress is a popular choice for those seeking a firm and supportive mattress on Amazon. This mattress is constructed with a unique adaptive foam that provides both comfort and support. The foam is designed to adapt to your body and relieve pressure points, making it a great choice for those with back pain. The mattress also has a cooling gel layer to help regulate temperature and keep you comfortable all night long.3. Tuft & Needle Original Mattress | Firm Support | King
The Sealy Response Performance 14-Inch Cushion Firm Pillow Top Mattress is a luxurious option for those looking for a firm king mattress on Amazon. This mattress features a layer of SealyCool gel foam that helps to keep you cool while you sleep. The cushion firm pillow top adds an extra layer of comfort and support, while the SealySupport foam provides deep down support for your body. With its plush feel and excellent support, this mattress is perfect for those who prefer a firmer sleeping surface.4. Sealy Response Performance 14-Inch Cushion Firm Pillow Top Mattress | King
The Linenspa 10 Inch Memory Foam and Innerspring Hybrid Mattress is a great option for those looking for a budget-friendly firm king mattress on Amazon. This mattress combines the support of traditional innerspring coils with the comfort of memory foam. The quilted memory foam layer provides pressure relief, while the steel coils provide the necessary support for a good night's sleep. This mattress also comes with a 10-year warranty for added peace of mind.5. Linenspa 10 Inch Memory Foam and Innerspring Hybrid Mattress | Firm Support | King
The Signature Sleep Contour 10 Inch Reversible Independently Encased Coil Mattress is a top choice for those seeking a firm and supportive mattress on Amazon. This mattress features individually encased coils that provide targeted support and help to reduce motion transfer. The foam layer on top adds extra comfort, while the reversible design allows you to choose between a firm or soft sleeping surface. This mattress also comes compressed and rolled for easy delivery and set up.6. Signature Sleep Contour 10 Inch Reversible Independently Encased Coil Mattress | Firm Support | King
The AmazonBasics Cooling Gel-Infused Memory Foam Mattress is a great option for those looking for a medium-firm feel on Amazon. This mattress is constructed with a layer of cooling gel-infused memory foam that helps to regulate temperature and provide pressure relief. The high-density foam base provides excellent support and helps to align the spine while you sleep. Plus, the mattress comes with a removable and washable cover for easy maintenance.7. AmazonBasics Cooling Gel-Infused Memory Foam Mattress | Firm Support | King
The Lucid 12 Inch Gel Memory Foam Mattress is a top-rated choice for those seeking a firm and supportive mattress on Amazon. This mattress features 3 layers of foam, including a top layer of gel-infused memory foam that helps to regulate temperature and provide pressure relief. The medium-firm feel is perfect for those who prefer a mattress that is not too soft or too firm. Plus, the mattress is CertiPUR-US certified for its foam materials, ensuring safety and quality.8. Lucid 12 Inch Gel Memory Foam Mattress | Firm Support | King
The Olee Sleep 13 Inch Galaxy Hybrid Gel Infused Memory Foam and Pocket Spring Mattress is a top contender for the best firm king mattress on Amazon. This mattress features a combination of memory foam and pocket springs to provide both comfort and support. The gel-infused memory foam layer helps to regulate temperature and relieve pressure points, while the pocket springs provide targeted support for different areas of the body. This mattress also comes with a 10-year warranty for your peace of mind.9. Olee Sleep 13 Inch Galaxy Hybrid Gel Infused Memory Foam and Pocket Spring Mattress | Firm Support | King
The Sweetnight King Mattress in a Box is a fantastic option for those seeking a plush yet firm mattress on Amazon. This hybrid mattress is constructed with layers of memory foam and individually wrapped coils for the perfect balance of comfort and support. The plush pillow top adds an extra layer of cushioning, making it great for side sleepers. Plus, the mattress comes compressed and rolled in a box for easy delivery and set up.10. Sweetnight King Mattress in a Box | Firm Support | 12 Inch Plush Pillow Top Hybrid Mattress