Ride quality can be seriously impaired by fitting harder and lowered springs. As the Uno is so light, it is particularly so.
Use the Lotus trick by fitting very
slightly uprated/ lowered springs but use uprated dampers/ shock absorbers as well. That is a far better combination than just fitting rock hard springs.
Don't forget that if you go too low you also upset the suspension geometry, especially the camber. This can be adjusted out by notching the hub to strut mountings, but failure to do this will lead to tyres scrubbing their inside edges and poor handling.
Also, fitting hard springs AND fitting bigger wheels with low profile tyres will not help. Low profile tyres have much less compliancy than higher profiles, so these will only add to an uncomfortable ride because they have less 'give'. In your case you've done both (hard springs and low profiles), so in a car as light as a Uno you've probably messed up the suspension compliancy. When your wheel hits a bump the whole car will 'bounce' and the wheel will leave the road momentarily rather than absorbing the bump as it was designed to do so. This actually leads to
worse roadholding!
The only thing you can do to improve the ride quality is to fit softer springs, and as mentioned above fitting uprated dampers as well should give you the best compromise. I would have suggested fitting the turbo anti roll bar like Dunc said, but you've already got one! I fitted one to my 45S with bog standard suspension and it gave me the best of both worlds. Ride quality was just as before, but the car no longer 'rolled' and was much, much flatter during cornering. Ironically it probably has better road holding than one fitted with harder/ lower springs but without a roll bar.
A front strut brace will help stiffen the shell, but don't waste your time with a rear brace. Unless the rear brace mounts directly onto the shock towers they don't work! This is because most of the rear braces you can buy fit onto the top of the shock absorbers and NOT onto the towers. As the shocks are rubber mounted it DOES NOT link the shell load bearing points, which is the whole point of a strut brace...
Your situation is very common, as it's the in thing to slam a car onto the deck and fit big wheels with low profile tyres. Unfortunately, the Uno's suspension was never designed to work that way, so having a bone jarring ride is the price you must pay for 'looks'. Either compromise the springing, or buy your rear passengers kidney belts
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