Memory foam mattresses are offered in a variety of thickness. Because feel is subjective and the level of support can vary from sleeper to sleeper due to weight and size, there really is no best thickness for Memory Foam.
The foam is offered in a range that can vary from 1 inch up to about 8 inches. Tip to keep in mind, anything less than 2” is a waste of money in our opinion unless it is replacing a low quality PU foam. You will definitely not experience the true “memory foam feel.” With thicker layers of Memory Foam Memory Foam you will get the well publicized experience the material has to offer. Lets face it its popular and selling because people like the feel.
To clarify I do believe that the more Memory Foam you have in ratio to cheaper, less durable foams the better and more long lasting the product will be.
Finally what it really comes down to is what feels good to you and what is in your budget. General rule of thumb, the more memory foam the higher quality the mattress should be so do your homework.