I am making the assumption that a bike as old as yours has a 1 inch threaded steerer. The steerer is the top tube of the fork that goes through the frame. Older 1 inch forks had the most rudimentary types of suspension. later models used a 1 1/8" steerer which are available and some were of good quality but unfortunately won't fit your frame. Even if you could find the best fork available at the time it would likely be showing its' age. The rubber parts in particular tend to harden with age and replacements if available bring high prices. You also need to be concerned with how a new fork will affect the bikes handling. A suspension fork will raise the front of the bike several inches. This likely to affect the bikes stability. You can try some less expensive thing first. Try lowering the front tire pressure ( high enough to avoid pinch flats but low enough to allow the tires to absorb some vibration), some thicker grips to absorb vibration, padded gloves. It will likely be more cost effective to buy a quality used bike that was designed for use with a suspension fork.