AmazonBasics Memory Foam Mattress - 12-Inch, King Size - Soft Bed, Plush Feel, CertiPUR-US Certified, Breathable, Easy Set-Up https://www.amazon.com/dp/B07C49S6CR/ref=cm_sw_r_cp_apip_hWfOt9IHBgyG1

The only caveat with this mattress(there are more options but this is the exact one I bought.) is that this bed is very soft so I wouldn’t recommend for people who sleep on their back, as it will probably cause problems down the road. I sleep on my side so I’ve always liked softer beds. Good luck!