Maybe you could go to a gym or PT place and test the types & firmness they have , or a sporting goods store...

I just got a bare bones generic one but it is from 2005 I think , now there are so many new styles..

You could test with a tightly rolled large towel or blanket too.
if too firm or too soft, it also depends on how severe your symptoms & pain levels are, what you can tolerate comfortably..

A tennis ball against wall or down on the floor worked well for me- easier to get into some of the triggerpoints than the larger foam roll edges... but some will always need a thumb or friend to get to them...