I've given up on using memory foam to sleep on, including pillows. They are too hot, they eventually get flat or get dips and they are not biodegradable. Instead I have opted to sleep on latex foam. What a difference! I love it. I have a 3" latex topper and also a latex contour pillow. I'm in heaven each and every night I get into my bed.
ETA-
Latex foam does not get hot like memory foam does. Latex foam is perfection.
Also, latex foam will last longer, much longer than memory foam and latex is more durable than memory foam.