I’m always cold so this is my area of expertise 
I just purchased some Kerrits crossover winter knee patch breeches and am very pleased with them. They are warm, comfortable, and well tailored. The fabric and styling is much less casual than there other styles–I wouldn’t hesitate to show in these during colder weather. They were hard to find and I can’t understand why Dover and Smartpak don’t sell them.
I also have been eyeing the FITS Kate or Beka winter breeches, and if they had come in tan I would have purchased a pair. (I specifically needed a tan pair.) I have the old style FITS winter breeches and they are wonderful, so I have confidence that FITS can make a great winter breech.
The Tropical Rider Toasties are very warm and plush and comfortable and well made, but the tailoring is very simple. I like them for super cold weather since they are quite warm. They are slightly less flattering than my other pairs of winter breeches but I’m sure glad I have them when the temps drop.
The Iridion wind pro winter breeches are also very nice and they seem to pop up on sale quite a bit. They are true winter breeches, but not as warm as the Tropical Riders or the FITS.
I looked at the Kerrits flow rise fleece breeches in a local shop, but they seemed to be thinner material than a typical winter breech, they didn’t strike me as a true winter breech, more of a spring/fall weight. If you returned the Ariat Artemis tights, you might not be satisfied with those. The Kerrits crossover winter breech is a heavier fabric for sure.