We do not have sour cream. I use a variety of substitutions: some (like yogurt) are healthier, others (like crème fraiche) are about the same. I do not use artificially 'low fat' or 'low cal' dairy products but, rather, those that are naturally lower. I prefer not to use foods with a long list of of emulsifiers and stabilizers on the label.
Not all products are available in all markets.
Crème fraiche is a mature, thickened cream. It has a slightly tart flavor, close to sour cream but a bit sweeter. Unlike sour cream it won't curdle if boiled and it can be whipped like fresh cream.
Note: You can make crème fraiche at home:
Mix 1 cup (250ml) heavy cream with 1/2 cup sour cream. Cover and let sit at room temperature 12 - 24 hours. Stir, cover again and refrigerate for 6 - 10 hours before using. will keep up to 2 weeks in the refrigerator
Substitutions: Greek yogurt, plain yogurt, (both lower in fat); sour cream
Greek yogurt is a very thick, very creamy yogurt, often made from ewe's milk in Europe. It's a bit higher in fat than regular, plain yogurt. Any yogurt should be added at the end of cooking time and not boiled or it may curdle.
Substitutions: Plain yogurt, (lower in fat) crème fraiche, sour cream
Fromage frais is a soft, fresh cheese, similar in taste to cream cheese but much lower in fat. It's smooth and creamy. It is not the same as Fromage Blanc.
Substitutions: Ricotta, cottage cheese, (both also low in fat); cream cheese
Fromage blanc has the consistency of sour cream with a slightly less tart flavor and fewer calories. It can be whipped to make it fluffy (sour cream can't be whipped) and is often used in desserts with fresh fruit. It is less tart than either Greek or plain yogurt.
It is not the same as Fromage Frais.
Substitutions: Greek yogurt, plain yogurt (both low in fat); crème fraiche, sour cream
Quark is the German equivalent to Fromage Frais.
A thicker version of yogurt made by straining all the the liquid out of plain yogurt. It will have the consistency, but not the flavor, of Fromage Frais or soft cream cheese (which are both sweeter).
Ricotta is a soft Italian fresh cheese, slightly grainy and naturally low in fat. It is used in desserts and pasta dishes
Substitutions: cottage cheese, fromage frais
Mascarpone is a triple cream, high fat Italian cheese; an integral ingredient to Tiramisu. It has only slightly less fat than butter
Substitutions: 1/2 ricotta and 1/2 heavy cream; crème fraiche