Welcome Barry. Two things will affect stiffness over and above the spring rate.
The first is the kingpin to bush friction. As you’ve realised, suspension travel is limited, but to make sure that your pins are free, grease the nipples half way up the stub axles with the steering on full lock each way. Make sure it doesn’t get on the brake discs. You may not have nipples at the top of the kingpins, but if you do, a small amount of grease or oil will help.
The second item is the shock absorbers. If they are originals, and therefore not adjustable, you will find an improvement in changing to adjustables. My car has AVO’s which I am very happy with. Others prefer Koni. If your shock absorbers have a visible method of adjustment, slacken them off completely and start from there. This is usually achieved by turning the adjuster fully anticlockwise.
