I slept on a memory foam mattress for a night. Thing is, I can't sleep on my back, or on my side. But when I slept on my stomach, I sank into the bed and found it hard to get breathing room. I kept waking up and having nightmares about drowning.
Instead, I have a mattress that has a 2 inch layer of memory foam over 5 inches of spring. It does the job.