Memory foam or pocket Spring and which firmness

Hi John We are looking to purchase a new mattress as our current firm pocket Spring mattress needs replacing after 10 years.I'm 6"7 currently weigh 15 stone after giving birth recently and my husband is 6"0 weights 14 stone.We looked at mattresses and I'm used to a firm mattress but after laying on some of the pillow topped memory foam eg silent night chantilly we are tempted to try it out. We have had a memory foam thick topper previously but found it sucked us into the bed and made us hot. The one we tried didn't seem to do that but we were only on it for a few minutes.Do we go for a springs/" title="pocket spring">pocket spring mattress or one with a memory foam top, we would like it to last a long time and we both suffer from back pains.Thanks