CiG
Approximately Infinite Universe
Asphodelus plays a genuinely convincing form of old Katatonia death/doom, with some other influences here and there. They're who immediately come to mind.
Ataraxy are a strange beast. They shifted from classic "old school" death metal to incorporating early death/doom influences and crafting that magnificent and quite original album. Hard to really recommend a similar band beyond just recommending the older bands inspiring them nowadays.
Some others you might like: