Next on the list for Mahler....

There is a superb DECCA 12 CD Box set of Mahlers syphonys 1-10, Richard Chailly superbly conducting, available at a super budget price. For about $30 you can listen to them all and then decide which you want to concentrate finding specific LP's of. I'm sure you will be pleased as these are excellent musically & sonically. Cheers & good luck.

Just checked on Amazon and the 12 CD box set Is now $95.98 new and from $52.88 used. Bit of a price hike, but If Its good It maybe worth It.

I feel that Chailly's style suits Mahler's work very well.
Chailly does an excellent job on the 2nd, 3rd and 5th. These are the works that stand out in this particular set. However, the rest of the set is really good as well.