I have not had much trouble with squalor either. The top 2 troublemakers for me are:
1) unrest - this sucks if you're Italian, everyone in italy seems to get thieves' guilds and they constantly infiltrate, you need 4-5 spies per city just to defend ;)
2) religious unrest - heretics & conquering muslims, enough said

Squalor is just a fact of life, it's capped at 80% and you just build public order buildings till you overtake the cap, no big deal. Remember to always upgrade walls/castle as soon as it pops up and you will be fine.