Do you use mods? Because even if you're normally averse to altering your game, nraas has a few cleanup mods that can prolong the life of a save far past its expected expiration date. Overwatch, Errortrap, and Debugenabler all help cull the accumulated bugs that can end up borking your game—they fix broken sims, delete unnecessary objects, reset lots, and probably a thousand other things that I have no idea about but are essential to the health of your save. They also allow you to perform these functions manually if you suspect something is off. There might be one or two other mods (Traveler?) that would help as well, without changing anything about how you actually play.