The Berserk Deluxe Editions, which are basically the omnibus versions in English, compile three volumes of the original manga into one hefty hardcover. So, the first Deluxe Edition contains volumes 1-3, which means it includes the Black Swordsman arc and the beginning of the Golden Age arc, up through the formation of the Band of the Hawk. The second has volumes 4-6, continuing with Guts' childhood, Griffith's ambitions, and the pivotal events leading to the Eclipse. It's a pretty straightforward mapping: each Deluxe book just bundles three regular volumes in order.
Honestly, the main appeal for me isn't just the chapter grouping—it's the larger print size that lets you appreciate Miura's artwork in all its horrific detail. The binding's also way sturdier than my old single volumes that are falling apart. If you're tracking specific chapters, you'd need to cross-reference with the original volume numbers, but functionally, each omnibus is just a continuous chunk of the story.