I've been working on some Battlefleet Gothic style houserules for a simplest-style campaign. My terrain table has a 3/8 chance of no terrain (barring the Exterminatus and Planetary Assault scenarios, which kind of need a planet). I also changed Nebulae and Dust Clouds to be zone effects (like asteroid field) instead of global effects - making them zones increases the tactical thought that goes into positioning. I also added a modified version of BFG's leadership rules; Ld values are generated for each ship at the start of the campaign as per BFG rules verbatim, but instead of the BFG rules for Ld tests, a ship trying to use Evasive Maneuvers, Directed Fire, or Damage Control must make an Ld test by rolling 2d6 and getting less than or equal to its Ld score.
The main thing, though, is that your mention of extreme attrition reminded me of a BFG campaign rule: when a ship is destroyed, you can get a free ship of the same type, but its leadership goes down to the minimum value (I think it was 6... don't remember). This gives you an incentive to maintain 'veteran' ships, but also prevents total destruction through attrition.