I used a program called Profimat from a German company to code 68k assembly on Kickstart 1.2. Most people however seemed to use seka ord devpac at that time. Profimat did include an editor and debugger. The disk was bootable and it came with a 70 pages manual that brought you up to speed.
Maybe you are completely happy if you get a classic commercial Assembler from eBay? There also were some freely distributable assemblers on the fish disks, but I can't remember details.
