I know M Mind warp is the preferred weapon for Death Knight and Aether dmg, but if I don’t have that yet, what are some decent alternatives?
It depends on your build, physical, aether, bleeding, vitality…
Theodin’s Scepter is good placeholder as it’s easy to get. Farming Theodin may also give you Mindwarp if you’ll be lucky enough. Also I assume you focus on aether damage.
Yes this.
Theodin Scepter with nice Attack Speed can be used.
It also has Default Weapon Attack Replacer 
Having been in the same situation myself - I simply used a Mythical Soulsplitter (which seems to drop like flies) and had forcewave maxed. This was sufficiently tanky to farm both entire Krieg set and a decent Theodin’s mace, at which point I was able to ditch forcewave and respec to near-final build.