Hi Jean-Pierre,

It is not too difficult to install a slider on a Roco Eurofima coach. There is a little piece which replaces the plastic part holding the slider and that kind of clips onto the bottom of the bogie. You then run the wire into the coach through existing holes and mount the axle contacts for the return.
Roco makes interior lights for these models as well, but you may choose to use other brands as well.

Roco makes two and four pole current conducting couplers. My preferred single pole couplers are the Viessmann ones which are based on the Fleischmann Profi Couplers. You would still need to install axle contacts on each coach for the ground (return).
Roco 40420: https://www.ewmb.de/imag...ges/RO40420_U01_1178.jpg

You can use any current conducting coupler, but unlike Maerklin coaches, for many, you would have to solder a wire to the coupler and to the light strip inside the coach.

For a few of my installs, I managed to find RailTop's AC slider, which is the same one used by Roco as their "Flusterschleifer", but comes with a base plate that fits the underside of the bogies and can be screwed into it (rather than glued). I think the slider (with the Railtop base) have become hard to find in the interim.

This one should work: Roco 40500: https://www.ewmb.de/imag...ges/RO40500_B01_7778.jpg
As long as it has the two holes for the pins on the underside of the bogie, it should work.

Regards

Mike C