Second Hand Baby Matress Preparation

[Lukesmum]

I just bought a used cot and mattress. It all looks to be in excellent clean condition. No stains or anything on the mattress. What can I do to the mattress to make sure it has no mites or anything living in it. Will I just put it outside in direct sunlight for a few days or should I spray it with something before putting it outside or should I just go and buy a new cot mattress?