Memory Foam Mattress with an Electric Blanket (or Electric Mattress Pad)
Safety - Flammability
There is no safety problem such as flammability with a decent memory foam mattress or topper (as contrasted with one of the cheap egg-crate type foams).
Memory Foam Durability with Added Heat
There seem to be two schools of thought on using heated mattress pads with memory foam. Some people say the memory foam mattress won’t support the body
properly if it is extra warm. Tempur-Pedic® states on their web site that they do not recommend using electric blankets or mattress pads because the “exposure
to direct heat over extended periods of time can cause damage to the TEMPUR material”. Tempur-Pedic® further suggests that if at bedtime your mattress is too cold, try turning up the bedroom thermostat for twenty to thirty minutes before going to bed. Once you are in bed, the mattress will warm up quickly in response to your body heat. If you do choose to use an electric blanket to warm your mattress before bedtime, we recommend that you turn it off after 30 minutes to avoid overexposing the TEMPUR material to high heat.
My personal opinion - not supported by rigorous objective testing
Several years ago, I myself spoke to the Technical Director at another one of the memory foam mattress manufacturers and he told me there would be no problems. I tend to believe this version because I personally have slept on a memory foam mattress with heated mattress pads for about six years now and I do not notice any problems. In fact, during cold weather, my personal opinion is that the support and comfort actually work better due to the extra warmth and I didn't like the "cold brick" feel. And I definitely do not want to increase my house temperature. One of the major benefits of heated bedding is to save money and energy by heating only the bed, not the whole house.
Since some memory foam manufacturers say no and some say yes, you will have to make the final decision whether to go with the heated pad on the memory foam. Sorry we couldn’t be more scientific or definitive.