Are the tomatoes that you're using pale watery and bland like so many supermarket tomatoes? Unless you have access to good fresh tomatoes you are probably better off using canned. Really they are good! And definitely superior to a mediocre fresh tomato. If you are cooking fresh tomatoes look for sauce tomatoes like Roma instead of slicing tomatoes. You may want to seed and peel them or you may not- just depends on the sauce.

There are so many different ways to make a flavorful sauce. If you are sauteeing onions and garlic first then try starting with the onions because they take longer to cook and you can extract more flavor from them without burning the garlic. Then again there are some tasty sauces where the garlic onion tomatoes and basil are all blended together raw and then cooked- so there's no one right way.

Various things to try adding- not necessarily all at once- tomato paste to thicken and add richness and color. Small amounts of sugar balanced with an acid like vinegar. Hot pepper flakes or hot sauce. Fresh herbs like basil added at the end. Chopped sweet peppers or mushrooms at the beginning with the onions. Capers. Olives added near the end. More salt. A little extra virgin olive oil swirled in at the end.

If vegetarian is not a requirement you can add fish sauce near the end, or you can sautee anchovy filets at the beginning- they will pretty much completely break down. Or you can cook crumbled sausage or beef or pancetta first and then cook the veggies in the rendered fat.

If you only have access to dried herbs and spices that's fine- in addition to oregano and basil there are marjoram and thyme and rosemary (use sparingly!). Fennel seed is a really good and flavorful one- to bring out the flavor it's good to saute seeds like this briefly in the oil before adding the wet ingredients, unlike the dry herbs which you would add much later.

If you're open to things other than Italian then you can try a sauce like the one in this recipe for shakshuka with peppers and onions and paprika cumin and cayenne pepper. Really tasty! https://cooking.nytimes.com/recipes/1014721-shakshuka-with-feta