Liner shorts can you get insulated

full weight shorts will be thicker material. they may be warmer 

Heavier weight baggy over them?

Looking to wear them just as a liner under winter riding trousers.

Why are you dismissing bibs?
Trickier comfort breaks?

I have some 3/4 length warm tights from endura. They are much warmer than a standard pair of shorts.

Something like these but mine are bibs- warmer at back and front and -3/4 lenght- less soggy round the calves

https://www.endurasport.com/fs260-pro-thermo-tight-black/12925969.html

Plenty of full length tights (leggings) made from Roubaix Lycra (fleecy inside) available. Most of the shorts made of roubaix tend to be bib shorts.
Tights keep you even warmer even though you look like a Kiwi backpacker wearing shorts over tights.

The only winter weight shorts i've seen are Rapha pro winter, but they're bibs and big money!

Thanks all

I’ve got some Howies wool liner shorts that get used when the snow is on the ground. They get so little use, you can see why the market for them might be small. The positive side effect of that is that’ll last me a lifetime.