Mattresses are available in variations of firmness, from soft, to soft-medium, to medium, to medium firm, to firm. Soft mattresses suit any sleeping positions, are known for comfort, and tend to be chosen by people without back problems. Firm mattresses, meanwhile, are effective in back support, and so are suited to those who require (or prefer) a less yielding surface.
If you suffer from allergies, it’s recommended to use a hypoallergenic mattress.
Many sleepers run hot, in which case they should consider a pocket sprung mattress, because they don’t trap as much heat under your body. You can even try mattresses with cooling gels. Again, personal preference plays a part.