who said anything about a broken spring... although that has happened to me before too, 1 coil snapped off and was jingling around in the strut (amazing it never fell out)..
Well hard to advise without being certain what is knocking, and most suspension parts look visually ok until they are completely fubar'd. To check them properly you need to apply quite alot of force, levering with a crowbar or similar to check for play in all the ball joints.. Do this with the car jacked up, and properly stable on axle stands - wheels off..
As you say your steering feels loose i'm inclined to suspect the track-rod ends without seeing it - if you wiggle the steering when the car is stationary can you hear this knock - albeit probably not as pronounced.
There is some argument however, if you want lowered spring to just changing the drop links and the track rod ends and spring all at the same time - after which proper wheel alignment. Or is that just because you don't like the current feel of the steering??
edit: worth noting that all these parts should be changed in pairs i.e. both sides of the car. And wheel alignment after track-rod ends or springs. Should be ok without for just droplinks.