First question: Do you have the Citadel Paint App? Might sound dumb, but there's handy basing 'themes' in there.
Second: Have you
looked at the Texture Paints that
GW sells?
Stirland or Astrogranite with a bit of Valhallan Blizzard might be a good call for you. A bit of snow can help break up the Ulthwe colors compared to the base.