Hi there,
Check out http://www.babesafe.com – there is extensive research that shows cot deaths are more common on 2nd hand mattresses. In addition to buying a safe new mattress, You could also get a mattress cover from them which will keep your baby safe from harmful substances which may be present in certain mattresses.
I had a cousin who died from cot death so we are very aware of it in my family and I have always wrapped my mattresses with Babesafe covers for my 3 children
It’s a non profit organisation and the guy who founded it has been awarded an OBE for his work,
Good to know about this stuff…