You can use creme fraiche as yogurt or as cream and cook with it, because unlike cream it shouldn't curdle when boiled. It's good for swirling on top of a thick soup.
The other higher fat lower carb lower protein option that will give some tartness is sour cream, which has recently been renamed soured cream, in case morons thought supermarkets were actually selling cream that had gone bad.. duh.
essential Waitrose soured cream 150ml, 68p and 300ml 89p, Waitrose/Ocado. Made in UK. 18g fat, 2.9g protein, 3.8g carbs per 100ml
Yeo Valley organic soured cream 227g 95p Sainsbury's, £1, Ocado, Tesco. Made in Somerset. 18.5g fat, 2.5g protein, 3.6g carbs per 100g
Bakoma smietana (soured cream) 175g 75p ASDA, Sainsbury's, Tesco Made in Poland. 18.0g fat, 2.3g protein, 4.4g carbs per 100g.
ASDA soured cream 150ml 65p and 300ml 85p currently on offer, 2 for 1.50 Made in UK. 20g fat, 2.8g protein, 3.2g carbs per 100ml.
Tesco fresh British soured cream. 150ml, 60p and 300ml 90p, Tesco. Made in UK. 18.5g fat, 2.4g protein, 3.6g g carbs per 100ml
soured fresh cream by Sainsbury's 150ml, 60p and 300ml, 85p, Sainsbury's. Made in UK. 18.0g fat, 2.7g protein, 3.5g carbs per 100ml
Morrisons soured cream 150ml 60p and 300ml, 90p, Morrisons. Made in UK. 19.9g fat, 2.9g protein, 3.8g carbs per 100 ml
Cowbelle soured cream, 300ml, 69p, Aldi. no nutritional info on mysupermarket.co.uk
Wloszczoma smietana (sour cream) 400g £1.25, currently on offer £1, Morrisons. Made in Poland. 18g fat, 2.7 g protein, 3.6g carbs, per 100g
mysupermarket.co.uk lists Tesco Finest creme fraiche d'Isigny AOC 250ml 1.10 but Tesco website doesn't so I have no nutritional info on that but will be imilar to the others from Isigny ie around 35% or 40% fat.
So soured cream leads to sour cream and chive dips which you will find fresh or jarred in many supermarkets. Our American cousins can make dips out of practically anything, but if you need recipe ideas, suggest trawling charity shops for 1970s cookbooks.