I’m no guru of prog, I lived through the original classical formalism and have the UK early pressings of ELP, Crimson, Yes, etc. But I tapped into "prog guru" Ken Golden who helped broaden my horizons, with good King Records reissues from Japan of some of the "important" Italian prog, and other things I found along the way (an Italian Polydor of DeDeLind, which sounds like Fado music meets Deep Purple).
Among them, an interesting obscurity out of Denmark, circa 1971, called Blast Furnace (band name and album title). An OG pressing will be spendy but it was reissued w/in the last five years- worth seeking out.
I also very much like both Cressida albums on Vertigo Swirl, from the period. Those will be spendy. I opted for a German pressing of Asylum, have the UK of the first album.
There are certainly different categories of prog, including pretty deep offshoots.
I really liked Ollie Halsall’s vibraphone-like touch to the guitar on the first two Patto albums (the US copy of the first record is more bombastic than the UK Swirl and far cheaper)- on their second, I’d say you need to look outside of the US for copies from elsewhere.