Who knows where I can buy some

Fleece lined leggings are lush and you could wear them underneath another pair of trousers. You'll be so toasty you'll be wanting to turn the heating down!

Wear long johns under your trousers or pj`s.
No one will see them and they are sooooo warm.

Cord trousers get my vote. Much warmer than jeans. Lands end do some with elasticated waist, I usually buy them with a discount code. Still not cheap but worth it.

I wear lined walking trousers from Costwold Outdoors or Millets. Great for walking the dogs, probably not so much for a coffee morning.

Cashmere jogging pants are heavenly, if you want to splurge!

Uniqlo have some warm trousers.

I bought some warm Bon Marche trousers 2 weeks ago. They are warm and cosy.

I wear jeans and thermal underwear every fall and winter. The only thing that can beat this combination is ski or snowboarding wear, but that's less comfortable to wear every day.
Though wearing pajama pants is an interesting idea, thanks for that, but still, consider getting thermal underwear like this. I would also advise some hiking socks as an option.

Layer up
Thick tights then leggings then trousers
I'm always cold!