A decent carbon seatpost at 27.2 diameter is amazing. Throw in a quality seat too.
Just over a year back I put a Red shift stem on and it was a game changer. Fantastic.
https://redshiftsports.com/products/...uspension-stem
That’s all good and helps but I’d recommend you also need to get yourself into a core stretching and strengthening program. Just add 10-15mins after each ride and after a couple weeks you’ll be much happier. Also make sure your saddle height is good too.