Pretty much you have one option
Scheel-Mann.
scheel-mann® orthopedic aftermarket seats for long distance travel since 1966. Made in Stuttgart Germany, it does not matter if your journey takes you to Starbucks or the Sahara, we have a seat to support you on the way.
scheel-mann.com
check out the Vario F XXL
Pricey but in the long run not so bad. They offer a model for those of us with taller torsos. I’m 6’3 with a tall torso and long legs and seats are always a problem. Found one racing seat in the uk that fits me. And only the scheel Mann seats offer one that will fit specifically.
Other than that you need a custom seat made or you have to get creative with what’s out there