I thought is was a couple of years ago, but a quick search showed I posted a one line comment about salopettes 4 years ago, so to share an idea against the cold.
Some years ago I bought a pair of salopettes (skiing trousers) from one of the cheap supermarkets, they were not very expensive, certainly less than a good pair of work trousers. I also see them in Charity Shops quite regularly as well.
In the recent cold snap, I've dug them out and have been using them in the workshop.
- Advantages: Outer layer is a hard wearing material, they have a elasticated cuff around the ankle to keep the snow (wood shavings/draughts) out. They will fit over ordinary trousers (or thermals) if you need them to and are lined with a thin but effective wadding, so are really nice and snug in the cold.
- Disadvantages: They have a waterproof layer in them, so if it does warm up a little, they can be more than you need.
For anyone suffering in a cold, draughty workshop /garage / shed I'd seriously consider investing in a pair.