When I'm not in the mood for my big rotational saves I usually pop into my Perrin family save. They're a couple I've been playing since early sims 3 days I remade in the sims 4. I usually have multiple saves with them but I always start them off living separate and seeing how they meet again, always playing her side and have him move in. I play them with aging off and have them experience whatever new feature while still keeping them in character. I ts3 they had a daughter and eventually died of old age but now I don't let them age. In some saves they might have kids, they might not. Their house will look different and their home world will change. I start them off rags to riches style and develop the house as they earn money, in a house lot or in an apartment.
To keep things fresh I make them friends in CAS, I never play them but I make sure they have full families, houses and jobs. I also made her parents and added a brother, I'll probably do something for him too but haven't been very inspired yet. Usually what ends up happening (and I hate that it's always the case) their house becomes too laggy because of all their collections and things so instead of moving them I just restart sadly. If I had aging on, it's like from starting a sim to when their kids are young adult. Back when I played legacies that's usually when I'd get "bored" but it wasn't boredom, it was lag and seeing how deformed the genetics made my kids look so I gave up on generational play.
Some other ideas, I had a barbie save back in ts3, basically playing barbie as a supersim maxing all careers. I made her a big pink mansion and would recolor everyone and everything in sunset valley in pink/turquoise/flashy pop colors. That's a good one for when you feel a little down. And then no really a rotation but playing all the premades. Aging off, pick a household and play them until you think they're "done", then move on to somebody else. I did that with Ned Whalen, made him climb up the tech guru career, then he decided to become a scientist, met his alien wife. Nowadays he's just the weird nerdy dad inviting people to barbecues. I moved on to other households, I'll never play them once they're done but it's nice that they are in the save, familiar faces and all that.