Me too and it's something I've become more aware as I got older. In short the lesson I learned is be well stacked and relaxed at the same time with the gaze forward. Also be able to freely move around around a fixed point if needed (the sit bones connecting to a sturdy surface of a chair). I find that swivel chairs or too soft of a chair could mess up stability/proprioception. A fixed/rigid chair at the right height helps me plant my feet better into the ground, forming some a sort of a tripod for better stability. Also an eye level monitor and a keyboard in reach without having to stretch out the arms helps keep a better posture. Another thing I practice is not leaning on the backrest too much. I noticed my kid shifting to bad postures when doing homework. Just gently telling him about it from time to time and making him be aware of his improved and what a correct posture should be seems to have improved his habits.