Get the DLC first thing (you already know you love Bloodborne and there's more of it out there to experience, so go for it).
As for the next game, I remain in the Dark Souls camp of best Souls game, but going back to that style of play will definitely leave you dissatisfied. That said, Dark Souls features the best narrative/lore, boss designs/encounters, and level design of the franchise and you'll always beat yourself up over why everybody tells you that it's an all-timer. Plus, it sports, IMO, the greatest post-launch DLC of any game ever (but that's mainly because it was supposed to exist in the base game but was omitted for budget concerns).
Also, Bloodborne was robbed. But not by me (GOTY 2015).