Perfectly clean mattress: no more chemicals

Remove the sheets and expose the mattress;
Vacuum to remove surface dirt.
The second step is the cleaning itself:

Mix plenty of baking soda with a little water in a bowl;
When you have made a paste, you can apply it to the mattress;
Scrub with a toothbrush and leave for an hour;
Brush again and rinse with a clean, damp cloth.
The last step is to dry the mattress as follows:
Dry the mattress outdoors or in the sun;
Sprinkle a little more baking soda over the entire surface of the mattress;
Wait 20 minutes and vacuum up all the baking soda dust.