Always nice to see folks hyping early Sun Ra
My favorite jazz musician and the early stuff is arguably best in addition to being some of his most accessible work. The 2 sets you mentioned are my favorites (the twofer is included on the list I posted) but "Angels & Demons At Play/The Nubians of Plutonia" and "Supersonic Jazz" are both also way up there. He also had a fairly accessible fusion period in the late 70's/early 80's- "Lanquidity" and "Sleeping Beauty" are the best sets from that era IMO.
Not familiar with Mehldau but I'd cosign the rest of these, though I will say that my favorite Ella is the early stuff with Chick Webb and that Billie Holiday is fairly accessible and arguably the definitive female jazz vocalist despite her limitations.