Thermal camisoles, vest, short sleeve t-shirts with a deep enough neckline to wear unseen under v neck jumpers?

[Flomasterina]

This seems to be an impossible ask.

I have found a few lovely ones in M&S, John Lewis, Intimissi, but all are showing in the v neck of my Autograph and Uniqlo cashmere jumpers.

Has anyone found this unicorn of thermal underwear and also what exact vests are you wearing with these same type jumpers?

Damart used to be very good for this.

Totally agree.
https://www.damart.co.uk/c-243540-vests-and-camisoles

Cashmere cami from LilySilk. https://www.lilysilk.com/uk/product/essential-cashmere-cami-top.html Pricey, but keeps you very warm. I wear mine all winter.