Like other reviewers have said, it is not 4 and you sink right through to the bar. Worse than the old innerspring I had on it. My solution was to simply use it as a topper rather than going through the hassle of returning it. This is what you should do. If the original mattress is still good but not thick enough, get a 2-3 foam mattress topper (without cover) so you can cut it to the right size. Then get a good bamboo mattress protector. Combined that will cost you less than $100. DO NOT BUY this as a mattress replacement.
Save Yourself Money - Look For another Solution
Like other reviewers have said, it is not 4 and you sink right through to the bar. Worse than the old innerspring I had on it. My solution was to simply use it as a topper rather than going through the hassle of returning it. This is what you should do. If the original mattress is still good but not thick enough, get a 2-3 foam mattress topper (without cover) so you can cut it to the right size. Then get a good bamboo mattress protector. Combined that will cost you less than $100. DO NOT BUY this as a mattress replacement.