Hi, I have just installed an interior carpet in my Twizy. It came from ELIA in Germany, http://www.elia-ag.de/ .
There are different colours and fits straight into the holes in the rubber mats, so easily fitted in minutes. Mine is lime green to go with 1 of my companies logo colours (looks like astro turf). £70 delivered direct from them.
They also do chrome side, front and rear bars and the full list of accessories are here http://www.elia-tuning.de/index2.php
Also check out their full blown Passion Version https://www.youtube.com/watch?v=Hf3SxDmS-dw.
Driving around a little less road noise and stops feet from slipping around when wet