Do you want to go solely hex for damage, or do you want a weapon but with something that casts hexes in your off hand?
If you want to cast hexes, you want the Black Witch Staff, which drops from the Witches in the Undead Crypt, as well as a mimic in Aldia's Keep. This staff allows you to cast both staff and chime hexes. I think there might be other things that deal more damage, but the versatility is more useful in my opinion. You can also carry sorceries and miracles with it too.
If you want to use a weapon, the Sanctum Shield from the first DLC, in the Dragon's Sanctum. Again, this allows you to cast everything, plus you can use a one handed main weapon too. You can't parry with it though, and it's only really useful for buff hexes, not offensive ones.
I wouldn't pair the two up however, as the black witch staff outperforms it as a hex casting tool, and the Sanctum Shield would be redundant.
Equipment wise, you should join the Pilgrims of Dark to get the Abyss Seal ring, and finish the questline to get some hexes.
Hang on, what magic haven't you leveled up, int or faith? You kinda need both for hexes, and to have them at around 30 each, although some specialist ones require you to go up to 40 (and I think one needs 60). You can work with less than that, but you'll be limiting yourself in your selection of hexes. Is there a reason you don't want to respec? You can get plenty of Soul Vessels throughout the game.
