Have you tried SPQR yet? if not then i give it my humble recomendation, not only is the senate present but they are given super-elite praetorian guard as their defence, which u cannot recruit till u conquer rome. The mod is very different from vanilla, not least in the fact that all units have zero recruitment times. But for overall strategy and logistics of your conquests it is second to none, and the battles are pretty good too :p

ps: House Rules for added depth and difficulty - difficulty=good