In addition to your room size, there are several other factors that can influence your needs. Your height is an important factor in your mattress size choices. Those under six feet tall can have any mattress, but those over six feet tall may not be able to sleep on a mattress less than 80 inches long. The number of sleepers sharing the bed is another vital consideration. Couples need at least a queen. Parents who co-sleep with their children can benefit from a king. Larger families who co-sleep with several small kids might even need an oversize king.