Definitely do NOT actively grind these for Backstory.

Do the sane thing and just use the Bone Market to sell to the Tentacled Entrepreneur. You'll get Final Breaths which can be used directly for Backstory, alongside Memories of Distant Shores. You'll likely have more Breaths than you even need. The Memories can be spent/upconverted to access the canals in Jericho Locks, allowing you to get Vienna Openings from Fiddler's Scarlet for additional backstory (plus reaching Doctore, or alternatively getting anything else you might want from the Locks)

If for some reason you happen to have a surplus of these, go ahead and spend them here, as there's little other use for them.