Living in Europe you should not have any trouble upgrading your 200E.
Everything you ask for is offered directly by Mercedes-Benz, as original equipment. Just visit your local M.B. dealer. The cloth seat cover is easily replaced and when done looks great.
You may fit an aftermarket electric window kit for the two front windows or all 4 windows. Mercedes-Benz offers them with all parts, cables, motors and switches included, and by M.B. standards, it is NOT really expensive. What might run you hi is on labor costs. The kit comes with the appropiate hole covers for the doors matching your interior upholstery.
Almost every extra offered by Mercedes-Benz can be retroffited aftermaket. Some are easy to do, other take a lot of time and money. The only ones that are too EXPENSIVE to think about are: electric sunroof, electric power front seats and auto transmission.
Not too expensive and might improve the look and feel on your car: rear foldable head-rests, rear electric sunshade, air-conditioning and new design light-alloy wheels.