Another small fix is specifically downloading Sims with assigned NPC jobs from the Gallery. It doesn't work every time, but I've noticed the game often using the Sims I downloaded for bartenders, cooks, waiters, detectives, etc, since they already have the job. Simmaddness has a bunch of households for NPC jobs. They're very Ken-and-Barbie-looking, but at least they're dressed well and have some variety.
For them to keep their jobs, don't enter Live mode with them. Place them on a lot then evict them. Or, select Create a New Household from the Manage Worlds screen, replace the auto Sim with the ones you want, save, then just don't select a house for them - they'll end up in the Manage Households tab as "Not in World".