Hi Jane, Thanks for the question!
At Winstons we would advise against electric blankets being used with memory foam mattresses as the heat from the blanket can make the foam feel very soft, which can result in people struggling to find the mattress comfortable as it is not firm enough to support them properly. Furthermore it is still debatable that the heat from the blanket could be damaging to the mattress itself, resulting in the mattress dipping and sagging, this has not be proven but is still a possibility due to memory foams heat retention properties.
However, with a mattress that is 100% natural latex, you can use an electric blanket as this type of foam is significantly more resilient. The latex mattress may feel slightly softer, but not as much as memory foam. The only side effect of using an electric blanket with any foam mattress is that it will be hot! All foam mattresses have heat retention properties, (latex less so), which means they will absorb all the heat from the blanket potentially creating an un comfortable sleeping experience, therefore would suggest you consider a 100% natural fillings mattress as they are much cooler option than foam mattresses.
Our Winstons Ultimate Hybrid Latex Mattress and our Winstons Premier British Wool 1500 Pocket spring mattress would be compatible with an electric blanket.