Per my *limited* understanding, a fresh hammer will usually fit, but MAY need final "fitting" on the engagement surfaces between hammer and sear. This fit is a critical safety thing.
In your shoes, I'd score another hammer from Brownell's, throw it in and do a THOROUGH "checkout" on it. Make sure it doesn't "push off", or still stays cocked when prodded/wiggled. Make sure the firing pin's protrusion is enough.
-=ANY=- questions on it after that means gunsmith time. Do not pass go, do not collect $200, get it in to the gun veterinarian el mucho pronto.
IF THE HAMMER CAN BE COCKED AT ALL (still has the "SA notch", which many do): It occurs to me that there may be a funky alternative. Drill two holes sideways through the back "curve" of the hammer you have now, and carve a solid brass or aluminum "thumbrest" which saddles over the back of the hammer and it attached with crosspins. Odd? Sure. But it would allow you to set the hammer thumbpad height and ergonomics to whatever you wanted, and if it broke...well, it's still going to work in DA mode regardless in a pinch.