Can you reccomend some thermal curtain linings

[Fluffycloudland77]

That aren't stiff and plasticky?.

The last pair I had were just too stiff and it made the curtains too bulky.

"Stiff and Plasticky" sounds like blackout lined curtains to me, they have a rubberised backing on the lining to prevent the light (and some cold) getting through?

Interlined curtains would probably be better, usually made to order, don't know if you can buy them readymade.

The curtains are interlined but they are going over a set of French doors plus a big window so I want the room to be well insulated.

It's really hard to get thermal with no blackout element.

Interlining comes in different "weights" from 410g/m2 to 160g/m2. The heavier the weight would stop more draughts, obviously.

We have these for our drafty, big old front door. They're quite thick, and feel a bit like satin, not plasticy at all. I have no other thermal liners to compare them too, but they made a very noticable difference to our hallway.

I have lined my bedroom and living room curtains with the cream fleece blankets that ikea sell for about £3 each. A bit of a budget option, but very effective at keeping the room warm and they let light through (important for me, as I hate sleeping in a pitch black room)

We did fleece at the last house (rental), it did work.

The curtains are 90 x 90 and I've found liners, dunelm mill do non-blackout liners.

I'm planning ahead for winter.

I've been using various linings for curtains for many years, and can now recommend fleece . I bought "thermal" curtains for living-room bay, needing something fast, but they were horrible to the touch until I made linings in faux-suede.
My bedroom curtains do need blackout linings, but I no longer have these gathered (weight),and have added another pair of curtains to improve insulation and appearance, which are much easier to iron after washing.
Interlined curtains would be my choice for french windows, but I'd have them checked for draughts.