McBTC Do you ride a road bike? If so, hopefully a less aggressive position may ease and perhaps eliminate the lower back pain. And if so, perhaps a stem extension would help solve the back issue...
I have a 2020 Trek Emonda SL6 and a 1995'ish Bianchi EL/OS NIvacrom steel frame with 2014 Campy Chorus (both road bikes). The Bianchi is relatively aggressive in its setup while the Trek is somewhat more moderate. WRT this problem I find the Bianchi slightly more comfortable than the Trek (and either one is more comfortable than just about any other activity or inactivity that I am likely to encounter.
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BCAC Your story is my fear - long and complicated diagnosis and recovery process. But since yours had a happy ending I guess there is hope.
dave