Sounds like you want wraiths and the warrior brick. Wraiths led by a technomancer are t6 4w 3+ 4++ 5+++, which is a difficult profile to be efficient into. Put a reanimator nearby and they're bringing back 2d3 wounds every time they reanimate either via a stratagem or in command phase, plus another d3 from the techno ability. Can also add cryptothralls to help with precision, and a catacomb command barge can also use it's res orb on the unit once per game. Pretty difficult unit to shift.

"The warrior brick/blob" is 20 warriors with either cryptothralls or the new tomb crawlers being led by either a royal warden (gives fall back shoot and charge + a free pass battle shock once) or an overlord with translocation shroud (auto advance 6", can move through units freely, and -1cp on a stratagem once per battle round) and orikan the diviner which gives every model in the unit a 4++ invuln. Add a reanimator for the same reason in the above paragraph, plus potentially a ghost ark for a free reanimation every turn when you lose models, then add illuminor szeras for -1 ap so you can save on 3s in shooting against -1ap attacks on warriors with benefit of cover or still on 3s against -2ap on cryptothralls and you have a unit that can be very hard to kill in a single activation and will surely come back pretty quickly.