I've been tying hairs onto rig rings (or swivels) for years for snowman rigs and pop-ups, and because I had to deal with crayfish which can cut dental floss, mono or fluorocarbon, settled on Kryston Merlin braid.
I found hair braid is too 'slippy'.
Any brand uncoated hooklink braid should work, but I bought loads of Kryston stuff when Dave Chilton sold the company.
I even go old school and have a loop at the end for a boilie stop for snowman rigs.
So I tie the loop at the end of the braid, and normally using a plain simple blood knot tie the hair to the rig ring.
There are occasional alternatives if I've been using single bottom baits or even wooden balls on the rig and they are tight to the loop and bait stop; I'll tie a dental floss or braid loop a pop-up onto the original hair loop.
Uni knot a loop, put your pop-up in it, and pull the loop tight. With the two tag ends tie them into the original hair loop with 4 overhand or granny knots, then lighter blob the ends to stop any pulling free.
A faff certainly, but it doesn't put fish off.
I've found overhand knots or granny knots can slip, but lighter blobbing the ends stops them pulling back through.