Don’t confuse proper sitting posture with a “straight back”. Your low back curve should be present and supported when sitting statically. Your spine should not be ‘straight”.
Be aware if you are bending through your hips vs your spine. Hip flexion while seated is not a significant risk factor for MSD, but spinal flexion is.
All “Ergonomic Chairs” are not created equal. Instead of “ergonomic” in the title, look for adjustability of chair height, seat pan length, lumbar support and back rest angle at a minimum.