Originally Posted by
Steamer
I have had luck using camping sleeping pad material (the closed cell resilient foam type*). It wants to run the full width of the seat so pressure isn't concentrated on and next to the spine. You could even layer it two layers thick (if your back likes the additional support in that location), but with the top layer being shorter and centered on the lower layer, to somewhat simulate a gently curved hump.
* I used this on one bike for additional, strategic padding:
https://www.thermarest.com/mattresses/ridge-rest-solite
Hmmm. My wife has a yoga mat in the basement that she might not notice if it went missing.
What do you think about this
lumbar brace? It's so cheap I just ordered one. It's always fun for me to order stuff from aliexpress because by the time it arrives, I usually forgot what I ordered, so it's like a present to my future self.