Better not to if you can afford a new one. A little google gives me this.
Is it safe to use second-hand baby equipment such as mattresses and sleeping bags?
Answer
Ideally, buy a new mattress for a new baby. It's been shown that there is a link between the use of second-hand mattresses and cot death. Sleeping bags (new or second-hand) are safe to use as long as they are the right size for your baby and the right thickness for the temperature of the room in which your baby sleeps.
Explanation
The link between second-hand mattresses and cot death is most apparent with mattresses which come from another household (for example, bought second-hand or given to you second-hand). However, there is still an increased risk of cot death if you re-use a mattress which was bought brand new for an older child in your own home.
It's been suggested that bacterial infections may play a role in cot death. Staphylococcus aureus (S. aureus) is a type of bacteria that has been identified as a possible cause of cot death in several studies. S. aureus has been found in used mattresses but it's not yet known whether the presence of this bacteria in used mattresses could be a direct cause of cot death.
Ideally, buy a new mattress for a new baby. However, if you need to re-use a mattress only do so if:
the mattress was made with a waterproof covering
the mattress cover is in good condition ? no tears, splits or holes
the mattress is firm, doesn?t sag anywhere and fits the cot without any gaps
you clean and dry the mattress thoroughly before use