There is one other infinte sleep source in the base game Dolores the Sleeping Arrow Puppet summon (you get her during/after Seluvis questline).
The Purple Lilies in the DLC are infinite they respawn in the south west tip of the map (the DLC also has two new sleep weapons (Thiollier's fist wepon) and Velvet St Trina’s Sword).
Magic infused Longsword or Broadsword should get more damage at high INT levels - they of course lack the sleep. Interestingly Velvelt St Trina’s Sword has slightly higher damage and an crit modifier of 110. You could powerstance the two but I don't know how sleep and eternal sleep build up interact together.
Oh, thought of one more stagger INT AOW Carian Sovereignty: it does more stagger than even a colossal can dream of and you can infuse it on any sword.