Velvet Blues tensions are supposed to be 25kg on every string. That's a couple pounds lighter than the figures we have for tuned-down Spirocore solos; solos are in turn a couple pounds lighter than weichs. The differences are greater on the bigger strings - all fairly close on G, but Velvet stays there while the Thomastiks get tighter, and by the time you get to the E string, the weichs are around 30kg.
These numbers are measured, literal tension exerted by the string at rest. There may be other parameters that are like tension - like, what if some strings are more elastic than others? that aren't so easily measured. I was interested for my bass, not so much my hands, so tension was really the issue for me. Also, we have several instances of different tensions reported for the same strings, so the relatively small differences may not be unambiguously significant.
Anyway, the numbers convinced me that Blues would be a good bet for a low tension string. They (also) feel more elastic and comfortable to me than Spirocores, but maybe that's just the tension. I can get sounds out of them with a bow, but don't need to, so am not the guy to ask. If arco were more of an issue, the Compàs 180 sounds like a great general purpose string, though I suppose more expensive than Blues. Blues have a weird kind of zing at first, but that goes away and they sound great to me - cleaner, darker sound than my old Spirocores. If I should ever wear them out, I'll probably think about guts, and then get another set of Blues.