In the 1990s the BBC music magazine had for a while a German version, I believe (or in any case I had a few issues that must have been a good deal, not some expensive import because I usually didn't buy magazines, even with included CDs). And I think they had a section or series "What to listen to after/if you like X?" with X being a famous/well known piece and the suggestions often considerably lesser known pieces. (Unfortunately, I don't remember any details and didn't keep the magazines)
In a time before or with only rudimentary internet this often had great suggestions, not only for beginners. (In fact for beginners there is usually so much to explore one hardly needs specific recommendations.)
Nowadays and in such a forum it is almost impossible to recommend/suggest something not already well known or suggested many times.
If you like Mahler's "Das Lied von der Erde", listen to Zemlinsky: "Lyrische Symphonie"
