I had several heavier winter flannels made a few years ago by Ambrosi. I hardly ever wear the dark charcoal. I would stick with medium and light greys.
As far as other options, I had off white/cream pants made up in a heavy cotton/cashmere blend by NSM. I love them. They look great with navy or any earth tone jacket. I would highly recommend getting something similar.
That trouser fabric looks lovely. Cream flannel would have been a much wiser option than the medium brown I got made last year - almost as versatile as medium/light grey, with a bit more visual interest.