Sitting with bad posture for long periods of time is not good for you. This is nothing new. Many people have switched to standing or sit/stand desks, which are great.
Another great option, perhaps even better than standing for some issues, is to put yourself in a half kneeling/high kneeling position. You can use your existing desk, but lose the chair and grab yourself a thick pillow or soft pad.
Just a few minutes, a couple times a day can have lasting effects.
Place yourself close to the desk and make sure you have a straight line from your knee up through you hips, shoulders and ears. Tuck your hips under you. Pretend like your pelvis is a cup of water, or IPA; Don't let any spill out.
- Tuck pelvis under you
- Make sure hips are square to the desk.
- Be as tall as you can from your knee up to the top of your head.
- Don't lean forward.
For many people you will feel a stretch down the front of your leg that is on the pad. When standing with both feet on the ground it is easy to "dump" you pelvis forward due to tight hips and thighs. In half kneeling your front leg helps keep the hips level from front to back.
Alternate knees every couple of minutes. Try this a couple times a day for a week or two and you will start to notice a difference in your alignment.