Best Mod for solo play?

[Suicide Junkie]

I'd have to reccommend trying Pirates & Nomads

P&N V3.1b The latest solo capable gold Version.

You can also add any AI that was designed for the unmodded game by using this AI Patcher (link) to convert them from regular to P&N.
That includes TDM AIs.

Note that playing as a "Normal" will mean the game is no harder than normal, but you will get lots of toys to play with.
Playing as a Pirate or Nomad race is where the big challenges come in Don't expect to conquer the universe, think of it as more of an RPG, where you and your party go exploring the universe while fighting off the hordes of Orcs and Phong and finding treasure. But mainly just trying to make a living in a hostile universe