I, too, had a hard time with Mahler in the beginning.
My 2 cents:
Start with the First Symphony-Way too many good recordings, so you have no problem finding a good one.
For vocal, I found Das Lied von de Erde, to be an easy listen- and it contains music from the 1st symphony, so you get to hear it in a different setting.
If you are still interested, move onto his other symphonic and vocal works.
Late Mahler is pretty strong stuff (like the Brahms Requiem-IMHO- Well, not that bad😉),
I found the 6th symphony by accident (Horenstein in Stockholm Live, if I recall). It is another ’easy’ listen.
B