I use my Twizy in sunny Barcelona, so I also suffer from time to time some heat related issues. My car is white with the black roof. In my case, I mostly feel the car gets hot when I leave it charging at the public EV charger, sitting in the sun. The back seat does not get as hot, and the wind gets in there much faster once moving. If your issue is the front seat itself getting too hot, I suppose you may try some kind of wooden bead seat cover. Not my style, but you may find some local shop that may do something with taste. If the problem is the driver feels hot when getting back in the car, I suppose the scoop solution for the roof, at the top of the driver head, may provide a nice breeze inside. It should be ease to install. Similar to aviation canopy scoops.