I'm not sure which would be best but the hake brushes normally found in art stores in the UK are goat hair. Make sure you look at how they're made, I'm sure some of the hake brushes available here are actually just very bad pastry brushes where the hairs fall out and ruin your coating.
Also if you're going for a more expensive process, try to get one with short hairs so there's less brush to soak up your expensive sensitiser, otherwise you can trim the bristles back a little after you buy it so they're shorter.