It shouldn't be that complicated to save a couple of different games! I find the auto save thing just complicates stuff. Last night I went to play, and just about burst into tears, because somehow, as well as the autosave, the game had saved my current save over a different one. I realised this because it has the file name (in my case, one called FOUR GIRLS) and under that it has the surname of the sim household. I went to play my Four girls save and realised it had a different surname, and sure enough, my four girls house has been overwritten somehow. That made me really, really cranky, as that is the save that I've mostly played. I'd spent a lot of hours getting their skills almost maxed, they were around level 7 in their careers, one of them had a child. Now the only save game from them is when I first made them and moved them into an unfurnished house.
I presumed that if you open a certain save, that the game would save over that named file, not another save. I always use load game, too.