Lowering Springs

Now I know theirs been lots of threads on this topic but I cannot seem to find definitive answers to my questions. So all advice, knowledge, experience and pictures would be greatly appreciated.

I have standard S-Line springs/dampers/18" wheels and find the ride pretty poor tbh. I know coilovers are the answer but they are beyond my budget.

So if I was to go for a set of H&R/Koni/KW/Eibach lowering springs would I be compromising the ride further or would the higher quality springs actually improve things?

Also can someone explain the sizing guide most springs are sold by? For instance if you look here http://www.dpmperformance.co.uk/audi-a3-8p-c-2375_2524_2533.html all the springs are described as 30mm, 35mm, 50mm etc. What does this measurement indicate? I'm presuming it's to do with the drop in ride height but as Sport, SE and S-Line models all have different ride heights which does it apply to?

A rough idea of fitting costs would be nice too, along with any pics of lowered cars on 18"s.

Thanks
Ron

Thanks but my motor's FWD only.

Thanks for putting me right Damian.

So by changing the springs the ride should improve (i.e. be a bit softer/more compliant) even with the extra drop?

I notice on your site springs are specc'd by engine size yet the 1.8t FSI engine isn't quoted. So if I were to go for a set of springs from your good-self which ones should I order? My car is a 2008 model, front wheel drive only.

Also are Eibach considered to give a softer ride than H&R/Koni/KW?

Thanks
Ron