ee Silk cane creek seat posts
https://canecreek.com/product/eesilk/
20 mm is not much motion..
Ergon seat posts
https://www.ergonbike.com/en/product...=43000025&s=cf
Or Titanium ... if it's bent a little it will flex more than if straight
and the choice of tube wall thickness can be customized for your weight..
...