Tooth brush bristles.
I have never had trouble with paint flaking off. Toothbrush bristles is almost all that I use. If it is an old brush, you can have some that are curved or if you use some from the middle, they will be straight. O0
Or, don't put them on. Seriously, at the scale of BT, an antenna would be so thin you wouldn't really be able to see it.Using wire and such will put it on, but that antenna is going to be as thick as your leg, if not thicker.