In reply to pebbles:
http://www.blacks.co.uk/womens/041695-peter-storm-women-s-merino-baselayer-...
£15... [hmm: I see only M (12) and L (14) seem to be available...]
I see these are a merino/polyester blend. I have a number of ALS/Peter Storm merino items, bought over a number of years. They started using MAPP merino (same as Arc'teryx), then moved to The Merino Company. No idea what the latest is. They seem as good as any merino, and as bad (i.e. not robust, subject to attack by carpet beetle larvae, etc).
The polyester blend will probably make them more robust.
I confess that, whilst I love the lack of pong that merino offers, their durability just isn't up to that of synthetics.
For -17C? PowerStretch. Or Primaloft...