Your babies mattress should be a firm mattress and not soft.
If the baby sleeps on a soft mattress before they reach 1 year of age the soft mattress could conform to the babies head and cause suffocation.
The baby might also turn over on the soft mattress and then suffocate as they would not be able to breathe and would not be able to turn themselves back over.
So never use any memory foam mattresses or any other soft mattresses in a babies crib.
Always use a regular baby bed or crib mattress that is made for babies to sleep on and the baby should be safe.
Also never put any crib bumpers, blankets, pillows etc in the babies crib after age 10 months to a year a baby can have crib bumpers.
But I would highly advise against crib bumpers because they can be used as a step for your baby to start climbing out the crib which could cause injury.
Once your baby begins climbing out of the crib they need to be moved to a toddler bed but I would recommend keeping the baby in your room until they are at least 2 years old.