Without mods, way to keep or make my sim "fine" all the time?

I know that you said without mods but there is a mod called meaningful stories that changes the way emotions work. The default emotional state is fine with the mod. I honestly cannot play without this mod. It makes emotions so much more realistic. Like they don't just get super happy all the time from being near items and furniture. Maybe that would be worth a try for you? It's a very stable mod that I've had no issues with what so ever for as long as I've had it in my game.