Foam has a four number system to tell you the quality and the density. The first two numbers are the quality, which can be anywhere from 12 to around 40. The higher the number the better the foam. The last two digits are density or ILD (stands for indent load deflection). The higher these two numbers the harder the foam. I like to use at least 65 compression foam for seats. Anything softer than that doesn't hold it's shape as well for any length of time, and doesn't support the edges of the seat cover as well. I would look for at least 22 for the first two numbers and 65 to 80 for the second two. So 2465 would be a good choice.
No one lives forever, the trick is creating something that will.