Most memory foam mattress covering is open cell foam to allow air flow and comfort. I think it would increase the chances of leaking.
If you have good idea why post your million dollar ideas here? Somebody will steal your idea and patent it and they'll be a millionaire. Not you.
To be a scientist you have to perform experiments and observe the results. Throw some oil and a 600 degree heat source on your memory foam mattress and write us a report.