First of all, what is tomato puree? It's a thick sauce of pureed, briefly cooked tomatoes that have been strained of seeds and skins; usually, there are no added herbs or seasonings (except salt). Tomato puree typically comes canned, and you'll find it with other canned tomato products.
You can substitute tomato sauce, with a couple of tweaks: First, cook the tomato sauce to reduce and thicken it just a bit. Second, check the ingredient list; often, tomato sauce is seasoned with herbs, vinegar, or other flavorings. If that's the case, you may need to adjust down the other seasonings in the recipe.