The VIP Supersoft is currently the only all-Supersoft toy in the Tantus line. That's not on the list, but it's definitely the softest.
I would say that the Pack n' Play toys are the next step up, since their construction is different. Basically, the harder inner core doesn't extend all the way up the shaft the way the O2 toys do; instead, the inner core of the Pack n' Play toys only extends about an inch up into the toy. The rest is Supersoft silicone. That way, you can pack them (in a harness underneath regular clothing) and they're still nicely usable when it's time to play.
I can't say enough good things about the Pack n' Play toys, actually. They're designed for packing, but are also a great all-around dildo. Nicely squishy, so if you want a softer toy they'd get my recommendation for sure.