I FULLY recommend the Claris Companion: https://www.clariscompanion.com/. It keeps things as simple as possible, and they provide tech support. I've used them for over a year now I think and I've been very satisfied. My grandfather is in his 90s and is able to use it in his care home.

The UI takes over the normal android UI to make things very simple. It also provides an email/messaging system which blocks out communication from anyone but the approved contacts, so there's no need to worry about email scams etc.

I'm not sure if they ship to the UK but they have a 4G version. But if you can get a 4G device, you could still use their app.

The key thing is absolute simplicity of interface and use, and this service is great for that.

Sorry this sounds like an ad, but it's seriously provided so much value to me in being able to keep in touch with and see my grandfather from 1000s of kms away.