Foam pipe insulation can be used to pad sharp worksurface edges. Remember, do not rest your wrists on anything while actually typing. Use a light touch. If you can't seem to break the habit of pounding on the keyboard, insert a soft piece of foam underneath your wrists to act as a shock absorber. Read the instructions for adjusting your chair.
Many chairs adjust in a variety of ways.
Fine tune the adjustments until your chair is comfortable for you. If you need a new chair, don't skimp. Although fully adjustable chairs are expensive, they are usually worth the extra cost. However, never buy a chair you haven't sat on and determined that it is comfortable for you. There are many companies that make universal claims about the ergonomic equipment they sell.