We’re big fans of good posture, whether standing or sitting.
If you must sit, we recommend chairs that have been designed with proper ergonomics in mind. Here are a few popular choices. For something that you’ll own for a long time and spend a large portion of your day in, the price is right.
You may see a lot of people promoting the use of balance balls or balance ball chairs in order to help with posture and “strengthening of core muscles”. It’s generally agreed upon now that the stabilizer muscles in the core will tire out quickly (~30 minutes) and you end up losing the nice lumbar curve you’ve been trying to maintain. It’s better to alternate between those balance balls with a standard chair (or standing) than to utilize one all day.