Sadly, Bohm only made the one Mahler recording: "Kindertotenlieder" with the younger Fischer-Dieskau. I consider it to be one of the greatest Mahler performances ever - and not just because of F-D. either.
Supposedly, close to the end of his life, he undertook study of some (I don't know which ones) of the Mahler symphonies. His close friendship with Leonard Bernstein had to have been an influence in that regard. But his failing eyesight prevented him from getting to the point where he felt he could confidently undertake performance of any of them.
Probably, Reiner's two Mahler recordings of M4 and DLvdE may be the closest we could ever get to hearing how a Böhm Mahler symphony performance might have sounded like. I would have been interested in what soloists Böhm might have selected for a performance of DLvdE.
Wade