At work, your computer chair should be adapted to your work surface. Therefore, it is important to raise your chair up so that your posture is relaxed and sustainable while seated behind your desk. You should adjust the height of the chair so that your feet are able to rest comfortably on the floor, with your thighs horizontal. A footrest will be beneficial if your feet are unable to rest on the floor.
The seat pan should be right below your knee cap height. Many computer chairs currently feature a pneumatic height adjustment where you can make adjustments simply by sitting on the chair or not sitting on it. With an older style of chair, you will have to stand in front of it and rotate the chair. But really, chairs this old should be replaced with a technologically advanced ergonomic task chair.
In order to avoid compressing the tissue on the back of your thighs and behind your knees you should be sure to avoid letting your feet dangle. In addition it can make the lower legs feel quite sore. You can avoid that unpleasant stress on the back of your knees by using a seat with a curved rim.
A good computer chair will have enough space between the back of your knees and the front of the chair such that a clenched fist can fit between them. You can lower the chair slightly if there isn't. Pressure may be relieved by tilting the seat forward, assuming you have a chair with that capability.
In order to support the lumbar area of your lower back, it is important to remember to adjust the backrest occasionally. It's very important to take care of your lower back, and this is the most important contact point. You will need to be able to adjust the height of your backrest, especially if your job requires you to sit in your chair for extended periods. Your back should get the maximum amount of support. Many backrests can be moved into a more forward or backward position. These features can be even more useful if the seat pan is deep.
It is always better to sit in a chair with good back support, particularly for long periods of time. If at all possible, make an investment in the best ergonomic chair that fits within your budget. If you still find your back to be uncomfortable when sitting in the chair, you should learn how to adjust a computer chair properly and then make as many adjustments as possible till you feel comfortable.