Hi,
As MrRB points out, all you need is a diode. It has to be connected with the right polarity, but that's it.
The reason this works is because you only need to clamp the voltage when the relay is turned off. That's when you see a very high voltage rise due to the coil back EMF. Using a diode provides a path for the current which greatly reduces the back EMF, so it protects the switch. And the switch does not need protection for turn on, because that's when the coil acts as an inductor and limits the initial current. The current then builds up to maximum over a short time period.
The diode should be rated for at least the current in the coil during normal operation. A 1 amp diode would probably be ok here, like the 1N4004 or similar.
The only time a diode becomes questionable is when you have to do super fast switching. Then you may have to use a zener or something else to allow the coil to discharge more rapidly.
An RC snubber is only needed when there is more complicated switching going on where you can not allow reverse conduction by a diode. Then you might also use a diode but the diode there would be for a different purpose.