I've been trying to find a firm mattress topper, but specifically something without the off-gassing and nasty chemicals. I'm a little sensitive (both psychologically and physically LOL) to synthetics and I just think that memory foam is way too warm. I'm on a full-size bed and wants something breathable that won't sag or soften up in a few weeks. Anything out there that meets everything I'm looking for? Or noooo?