After some doubt I decided to order a Cruise control. I ended up with a GoldCruise AP 300, specifically for the C1:

As I controller I choose the CM-25, because it can memorize 3 speeds.

So all this has to go into the car:

I started out with the clutch switch. What you have to do is remove the standard bolt which determines the height of the clutch pedal and replace it with the new one which contains a switch. This allows the cruise control to detect when the clutch is pressed so it can release the throttle.

Next is the brake detection. Because there is already a brake pedal switch in the car (for the brake lights ;) ), you can just connect the wire to the existing switch. So remove the connector and splice in the extra wire.

One of the other signals the cruise control needs is a speed signal. This can be found on the multiplug inside the dialunit.
Remove it and solder the speedsignal wire to the wire comming from the cruise control (it should be the brown/white wire).

As this is a point where I get a lot of question, I've added the picture that is in the installation manual below, indicating the wire.

I put the control unit up on the side of the driver footwell, at the outside of the car (it is a bit hard to see on the picture). It looks like a good spot for running the cable to the enginebay and to the controller.

Next is the installtion of the throttle control. First I hung the vacuum unit from the left strut tower.

Then mount the adapter unit from the throttle contoll so you can attach the throttle cable that comes from the vacuum unit. First remove the nut from the central axis.

Then place the extension bolt/nut.

Now the extra throttle lever can be placed.

And the last step, place the extension plate and run the throttle cable through it.

Then fixate the throttle cable. Don't forget to put some tiewraps over the throttle cable so it won't hit the engine.

Now route the air hose towards the right side of the engine bay to the vacuum hose that is situated there.

Now cut the vacuum hose.

And insert the T splitter.

And connect the air hose to the T splitter.

Last the controller needs to be installed. The hardest part is drilling the hole in the right spot. I sacrificed one cover to get it right, fortunatly they're not very expensive. Remove the cap, drill a hole and put the controller through. Then run some wires and you're done.

Before the cruise control will work it needs to be callibrated. The documentation is pretty good, so just follow the procedure in the manual and you should be fine.

I like the cruise control a lot, especially the preset speeds. The +/- reaction isn't that great, but the presets make up for that.