Yes, a soft mattress is generally considered to be the best for a baby, but make sure it's not too soft. An extremely soft mattress is generally not recommended for babies, as it can provide them with too much cushioning and may put their airways at risk. While a softer surface may seem more comfortable to infant sleepers, research suggests that infants should sleep on firmer surfaces due to the increased chance of developing Sudden Infant Death Syndrome (SIDS).