Mattresses range anywhere from basic foam mattresses just 4 inches thick to deluxe pillow-top mattresses nearly 2 feet thick. According to US-Mattress.com, the average mattress is 14 inches thick. Therefore, an 8-inch mattress is far below average. However, it is comparable to the average 9-inch mattress sold back in the 1990s. The difference in thickness is because the thinner mattresses do not provide much space for comfort materials in addition to springs.
Some people make their mattresses appear thicker by adding a mattress topper. Memory-foam and down toppers are two of the most common types. Adding a topper above a thin mattress helps make it more comfortable and gives it that extra height to make it look more luxurious. Therefore, if you end up with an 8-inch mattress but would prefer a thicker one, a mattress topper helps.
Most sheets are sized to fit mattresses up to 14 inches thick, or sometimes a little larger. Beyond that, the sheets are not deep enough. Therefore, if you have an especially thick mattress, you need to buy special fitted sheets with enough fabric to reach all the way down the side of the mattress. On the other hand, sheets on a thinner 8-inch mattress might extend several inches onto the bottom of the mattress because they are designed to accommodate thicker mattresses.
Although an 8-inch mattress seems to be a bad thing these days, it can actually be advantageous in some circumstances. For example, with a trundle bed, the mattress can rarely be thicker than 8 inches because it needs to fit under the upper bed. An 8-inch mattress is also helpful on a top bunk because it keeps the person sleeping there farther away from the ceiling and ensures that the guard rail still extends above the mattress.