First check your suspension in the garage! Second - the brand new suspension isn't very comfortable either! You would probably be better getting european shocks and springs (for the UK starlet or even German starlet -) ask in the local garage what they've got) - for the UK roads!
WE have pretty bad roads in the UK and those cars were designed for Japan - where they have very good and smooth roads!
Also, the cars are pretty light and no matter what suspension you've got you need the pressure to put on the wheels/springs - try it on your car - put 4 heavy blocks in your car and feel the difference in suspension!
What I don't like about Starlet's is the noise and the plastic inside the car - as all I want to hear is an engine noise - not the road noise or the plastic rubbing something somewhere in the car -( Apart from that - standard suspension is pretty good - for smooth straight roads -)
Standard replacement would be around £200 for springs and £150 for shocks -) Original Toyota - so I don't think you really need it -) just try to get a decent used one -)))) like a fresh import car - better if you actually sit in the car and try suspension -)
seriously dude what on earth are you on.
new springs and damper will improve the ride qaulity and handling, as has been stated the stock stuff is over 10 years old now and well worn,
KYB make the springs and dampers for toyota OE for the starlet so if he were to buy kyb springs and dampers they will be exactly what toyota will sell him.
also suspension technology has evolved quite substantially over the past 10 years since starlets went out of production, and kyb put all there latest technology into all there products,
and as for putting weight in the car, honestly how silly.
toyota designed the car to be a certain weight and designed the suspension to suit that, you will find that the starlet rides the same as any other car of the same age/era,
another way to improve the comfort belive it or not is to stiffen the body and make the suspension do the work as it should, this is what a lot of modern cars are like now they have stiffened bodies to improve ride and handling.