Saw a couple of discussions on using a sim card in the car a while ago, Money Saving Expert currently have a deal at £1.15 a month for five months (£4.90 after) with Lebara for a 5GB sim card. At that price I bought one to try, plugged in and worked it with no fuss other than selecting the network.
 

Isn’t you car able to use the data connection from your phone via CarPlay/Android auto. Mine does?

Yes, but this comes with free data roaming for the EU and also seemed an easier option for others to use the cars wifi, also it is a spare phone as it is not unusual for me to forget that I have left my phone in the van.