Need help choosing a new mattress; memory foam vs latex.

[clara10]

My landlord provide me with an old mattress, needed to change it fast!
problem is I've never bought a mattress before. Went shopping yesterday, was totally confused with what's in the market.

So I really need feedback. I'm thinking of getting a mattress with innerspring, but cant decide on having memory foam or latex as the upper layer. Please help. Which is cooler? Oh I need a firm mattress. Would really appreciate reviews...