Thanks for your question on Health Care Magic.
I can understand your concern.
No need to worry for this.
Dettol does not cause effervescence and hence no fumes.
You are only taking smell of dettol.
It is not harmful for the body.
Dettol is harmful if applied internally or on mucosa like in mouth, vagina, Penis, nose, ear etc.
No need to worry in your case.
But if you develop coughing, breathlessness,
chest pain than
consult doctor. Otherwise no need to worry.
And yes, you should change the mattress.
Hope I have solved your query.
Wish you good health. Thanks.