Satnav or phone? Which is best?

I am looking for advice.  My wife and I are not good with 21st century technology.  My wife has never managed to find her way round how to use a computer and struggles to remember how to send a text or make a call on our mobile phone.  In fairness to her, we use the phone so infrequently that several months can pass between the rare occasions we use it so it is easy to forget how the thing actually works.

However, we face a challenge.  In recent years we have found it increasingly difficult to find caravan sites in France which are listed in the ACSI guide.  We have satnav in our car (brilliant) but it does not accept map co-ordinates so is no help in finding French sites.   Our children wish we would buy one of those phones which will work for email when we are away in the caravan.  We are hesitant on spending the money for something which we cannot imagine we would use more than  a few times per annum.  On the other hand I seem to remember that some people are able to use satnav on a modern phone.  Does this mean that you have to purchase a separate programme/software (if those are the correct words) or do some phones come with such a facility already fitted?

It seems to me that we have three choices. 1) Purchase a separate satnav machine with European maps and the ability to accept map co-ordinates.  2) Buy a phone which will work for satnav - that is if such a thing is available.  3)  Buy both a phone and a satnav machine.  Obvioulsy the third option would be very costly and probably way beyond our affordability.

Other people's comments and experiences would be helpful, not least from those of you, like us, who were war babies and struggle with the digital world!