In reply to ClimbingJson:
I keep a pair of thick thermals and thin thermals You can then choose on the day depending on weather and planned activity worn either under soft shell or hybrid waterproofs, both were got off sportpursuit, decathlon should see you right though.
if it’s really cold and I’m expecting to stand around a lot I do have a power stretch pair but rarely use these as I run quite warm.
be aware a lined trouser might not work so well with a pair of thermals it could restrict your movement slightly and if you apply the principal of marginal gains to a big Scottish day out probably best avoided.