The big problem I had was getting glue on them without the chenille fibers clumping up. I made a pile of rather two-dimensional conifers before I gave up on it. Maybe a spray adhesive would work better than dipping them in watered down white glue.
For 10mm I would get some of the giant chenille stems, cut them to length, then trim the fibers to get the cone shape. Or look for some cheap bottle brushes and trim them.
I
can get chenille here in the UK, but the stems are more commonly (and familiarly) called 'pipe cleaners'

I can't find any of the wavy 'bump' types above 15mm diameter, which seems a bit small even for 10mm; but I found giant examples of the straight types - half a metre and 25-30mm diameter! (It's like a whole new world of hobby supplies!) Should do very nicely if I follow your advice and trim segments into cones.
I was wondering about clumping myself, specifically brushing or even combing white glue in to make it mat together, like stuffed toy fur for thatched roofs. 'Style' it into slightly more defined 'branches' for the flock? Just a thought that I might try myself.
I haven't forgotten the broadleaf method either. Thanks again!