After the first night sleeping on a memory foam mattress I felt unwell (sore throat, fussy thinking and general feeling physically low). Slept for another 4/5 nights and symptoms continued. Began sleeping on normal mattress and felt fine thereafter.
The memory foam is a chemical combination and some are treated for microbes. These mattresses ‘off gas’ for possible a few years and whether someone responds negatively immediately or not, the chemicals have to go somewhere! The second point is you are likely to feel much hotter while sleeping and this could be hard work in the summer time.
I would not recommend sleeping on a metal sprung bed either because the metal springs create and emit a measurable magnetic pulse. I think the best bet is a futon or mattress made of a natural substance. I would also not sleep on a mattress with an electric blanket still plugged in the socket.