Hi Elisabeth,
There are some comments about edge support with foam mattresses in post #2 here and the posts it links to.
The Brooklyn Bedding Signature (Best Mattress Ever) uses a polyfoam core of 1.8 lb density, but at a higher 36 ILD, so it may feel just a bit firmer around the edge. But just like in an innerspring mattress with a polyfoam edge support system, this only goes about halfway up into the mattress, and then the top comfort layers of materials will have a great impact upon the overall “edge feel” as well.
Phoenix