What’s the best way to use Colman’s mustard on a sandwich?

I love mustard on sandwiches, but I like to slather a whole layer of it on the bread. From what I’ve read, Colman’s is strong and should be used sparingly.

Would it be better to spread an extremely thin layer of the mustard straight up, or mix it with some mayo or sour cream to neutralize a bit of the spice but still make it spreadable?