Never used Black Widow but everything I read says that Tourna Black 7 is the most similar string, so worth a try. Tension loss is not as bad as I would have thought from reading reviews, and I've switched to this string from Silver 7 Tour.
I think your best options are Tier One Black Night, Volkl Cyclone, and Head Lynx Edge. BHB7 is similar to Black widow but in my experience has worse tension maintenance.
HGS is quite nice…so is mayami tour hex and tier1 black knight. HGS 1.25 mains with smooth round copoly cross (i like polaris) is very soft and arm friendly