The Sentient Sword is a much more effective tool for collecting Demon Will than Soul Snares could ever hope to be. It may seem weak at first, but it is powered by the Wills you carry, so crafting a Tartaric Gem is a must.
Note that the sword, as with all Sentient Tools, can be repaired with Crystallized Will in an Anvil.
This sword will serve you well.
Note that you can update the sword's stats by pressing [ПКМ] when you have it equipped - if you have recently acquired a large amount of Will, or perhaps are trying out a new Aspect of Will for the first time, then this may be a good idea.