Spirit
No, it is not safe ...
Polyurethane Foams are emiting strong toxins for a long time ... it is far from safe ...
Better uncomfortable but natural, then comfortable but toxic ..
Good natural materials for mattress are:
- cotton, linen
- woll
- animal pelt
- non-aromatic dried herbal materials like halm, dried grass, dried wood wool
Dried grass (mountain grass) placed inside thick cotton bag makes perfect, non-toxic and also very cheap mattress ... but you may need to replace the grass every few weeks or months ...