3" Memory Foam topper here.
My wife and I just purchased a very nice new bed - very premium - and I am so attached to the memory foam on our old bed, I decided that the new bed would be better with the foam. It is, even though the bed is waaaay too tall now.
No issues at all with temperature. I wouldn’t have anything else.
I liked the memory foam, but my bf complained so much about the heat that I tossed it.
This Bed is the one Mrs. Jockey and I recently purchased (had to skip fall vacation to do it 
) but after years of regular (and some feather for me, as she’s allergic) beds, the foam wins the day.
This bed is all foam, no springs anywhere, foam from top to bottom and it’s the most comfortable damned thing I’ve ever slept on, plus, it’s a no flip. All that and a 30 year warranty to boot (first 10 not pro-rated).
I’d say go with the foam, best you can afford, you won’t be sorry.
I got the heaviest, thickest foam pad on overstock. I love it, my husband loves it. I cannot spell enough nice things about it.
We wound up getting the 2" pad. It helps, but it’s not enough. We also cannot afford another bed, since this back breaker is less than 2 years old. Also, the pad does make the bed much hotter, not in a good way. Is this true of the full mattresses made out of memory foam?
Someone mentioned the egg crate foam. That’s not the same as memory foam which takes longer to spring back to its original shape.
Rubystreak, I have the full mattress and base support in the TempurPedic. I’ve never had a problem with its feeling too warm to me, but I think I have read in their materials that it does absorb body heat.
These mattresses are very firm, but they mold themselves to your body slightly.
catsix, no one could sink far into a TempurPedic. And I would just love to see someone sink six inches into a 2" pad!
Just a note: hospitals don’t use egg crate mattresses anymore (American ones, anyway). We use air mattresses, mostly. (very different than consumer ones)
We got a memory foam for my son from Overstock. He hated his mattress and actually preferred to sleep on the floor. He loves his bed now.