It’s very possible. The main way you have a reaction to latex is direct contact between your skin and the material. Since your mattress is covered by a couple of layers of cloth (your mattress protector and sheets), you might have some protection while you’re sleeping, but there’s still the risk of contact when you change your bedclothes or if the sheets slip off. Because of this risk of exposure, if you’re allergic to latex (and especially if you’re at risk of anaphylactic shock), it’s better to choose a different material. Memory foam mattresses can give you a similar feel to latex foam ones without the risk of triggering your latex allergy.