Don’t sell yourself too short here, you are definitely walking in the right direction already 
Now I have no idea what a DK plays like in WoW exactly, but if you are looking for a total tank with a vitality dmg theme then the Blood Knight set is probably a good way to start.
My first tips regarding your buildcrafting would be to:
- try and fully work around 1-2 main skills to maximise your build’s effectiveness (this is true 90% of the time). E.g. the main skills supported by the BK set are Counterstrike & Bone Harvest; the latter is a great nuke skill that I’d try to focus on here much more.
- Therefore, things with +to skill X are often even more important than e.g. OA/DA; though you still have to somehow reach your threshholds like ~3k OA/DA, of course. Thus, taking a relic like Uroboruuk’s reaping for its +1 to necro is very much worth using here.
- RR is the king! And this is especially true for a DK that only has 1 source of vit rr to start with. I’d strongly recommend going for two rings with -%vit RR like Cursebearer+Signet of the Fallen here.
This is a somewhat outdated DK Blood Knight build I found which you might take some inspiration from (many things have changed since then I’m afraid, so don’t be shy to change things up): [1.0.6.1] Crimson Soviet: 2H Blood Knight, 4buffs/no banners Cruc. 150-170 in 10 min. (Death Knight)
A few notes on this specific build:
- Ghol’s Reach gloves (FG item, not in the 1.0.6.1 guide yet) are probably BiS for Bone Harvest setups now. Taking the Ghol’s Medal on top of this for the set bonus is likely worth it, too.
- A well-rolled Korvan Reaping Halberd might also be a substantial upgrade if you have one (–> https://www.grimtools.com/db/items/13684)
- Since Foul Eruption from the RE skill is, unfortunately, pretty bad, and taking Manticore devotion for flat RR is waaay outdated I’d suggest working in Revenant instead.
I hope this helps a bit!