Hi zexpress,
The edge support in your BME was probably related more to the firmness level you chose (soft) than to the mattress itself.
Most foam mattresses don’t have or even really need side support if they have a support core that is firm enough and the comfort layers aren’t too thick and/or soft for the person sleeping on it. Having said that … there are exceptions to every rule and there is more information about edge support and foam mattresses in post #3 here and in post #33 here. With a foam mattress that is a suitable firmness level relative to the person sleeping on it (both in the support core and the comfort layers) then it normally wouldn’t be a significant issue for most people unless you often sleep or sit with most of your weight concentrated on the very outside edge of the mattress although the outside edges of a foam mattress would generally be softer than an innerspring mattress that has a specific edge support system.
The only way to know for certain whether the edges of a foam mattress will be suitable for your specific body type and sleeping style or your preferences will be based on testing the mattress in person (or a mattress that is fairly similar) before a purchase or by actually sleeping on it (if you can’t test it in person before a purchase) and of course if you are uncertain whether you are one of the few that may “need” or prefer firmer edge support then a good return/exchange policy may be a more important part of your personal value equation just in case the edges aren’t firm enough for you (regardless of whether they are firm enough for anyone else).
Phoenix