[Susan66]

I do an even simpler version. I process the tomatoes by cooking them until they juice up, use an immersion mixer to blend everything together, including seeds and skins. If the resulting sauce is really watery sometimes I will stop at this point until the water rises to the top. (Refrigerated) I usually just pour or ladle the water off the top and use for soup base or canning beans, if there are beans enough to can.
Then I reheat the tomato juice, fairly thick now, hot pack it in sterilized jars and water bath it for 15 minutes (per Stocking Up, Carol Hupping Stoner, ed. Rodale Press. My copy is 1977 edition. )
Most tomatoes are high acid enough that you don't have to worry about adding vinegar or lemon juice. I never worry about mixing varieties- when I start canning, I put all the kinds in together. Paste, slicers, cherry types all. Like Bakedin, I worry more about losing vitamins than reducing the sauce- that takes way too much time for me. I hate wasting the juice/water though. It's full of vitamins, too.
I also can tomatoes without saucing it- dip in boiling water for a few seconds, drop in cold water, slip the skins off, cut them up and toss in the pot with a little water. Cook them up, boiling about 10 minutes or so, put in the jars, and process in the hot water bath for 15 minutes. If the fruit is put raw into the jars is when you have to process for 45 minutes. If you dislike seeds (and many do, they are a little bitter) squeeze them out as you put the tomatoes in the pot and discard. Or ferment and save them!
I've been canning tomatoes this way for about 50 years.
I don't buy commercial sauce. I generally have so many tomatoes that I can them as the best way to preserve them. I never add salt. It is not necessary, and these days I am salt sensitive. It's the acid in the tomatoes that makes them work for hot water bath canning. I admire people that go to the effort of cooking up the sauce with all the other stuff in them, but find it to be not right for me. I've done it but no longer bother. I do occasionally use the pressure canner, for other produce. Beans, if I have a great crop. Mock mincemeat. Most other veg. I prefer frozen.