Greenstuff is relatively soft imo. Soft/firm does probably not matter that much – it’s more a matter of preference. I got this one from boesner (they don’t sell this exact model anymore but it was a size 2) I am really happy with. I cannot really compare it with anything else. It’s neither extremely soft nor stiff if that helps. Never had the desire to go smaller. For this I use metal tools.
Since writing this post I have been incorporating metal tools more into my work flow. Problem here is what’s currently out there (not naming brands here but just type green stuff sculpting tools etc into Amazon) is utter crap since GW retired its relatively decent sculpting tools a few years ago. I now use almost exclusively student-grade dentistry tools (which have the same shape as the old GW tools but a better finish. You can find them under the names Hylin/Le Cron/Zahle). If you have trouble finding vendors selling to private individuals, drop me a message… I have been trough this. Talking about domestic made tools here. There is import stuff on Amazon/ebay that may be ok as well.