Earlier quoted context omitted.
Not sure this is good advice. I like a firm mattress, but IKEA mattresses are absolutely terrible. I also cannot sleep with a foam topper on any bed. They're hot and screw up my back beyond belief.
Ikea sells different types of mattress (spring, foam, latex), each with different thicknesses and price points. I've bought ~10 Ikea mattresses, avoided the cheapest ones of each type, and been pretty happy. I can understand why a foam topper would feel hot. It's main purpose is to provide a sleeping surface that's the same shape as your body, so of course this means it maximises the amount of contact between you and…
You've bought ten mattresses from them?! In how many years, and for how many people?
I don't think my parents bought ten mattresses in the 20-odd years they had their four kids living at home - and I still sleep on one of them.
Personally I don't trust anything from Ikea anymore. Their quality is such garbage for all their products from furniture to glassware to lamps, I can't give them a dime of my money knowing whatever I buy won't be around next year. Multiply whatever you were going to spend by 1.5 and go to a decent home store, or just go to Target instead.