Landline To Mobile Router Voip Service Uk

Hi all.. Hope this is the right place to ask this question.

My mothers landline is no longer accepting inbound calls due to line issues that are not going to be resolved due to the imminent switch off.
Ideally I would just switch her over fully to a mobile network. I can get her a Lebara contract for all her needs for £5 a month. However, she is in her nineties, partially sighted and struggles with mobile phones.

The company she uses for her landline (SimpleTelecoms) offers a special router, plus sim that just connects to mains power and to her old landline phone. She can use this through a mobile network and it performs just like her old service. They will even port her old number.

Her old landline was £26 a month for an evening and weekends deal. This Phone2Home service is just £16 a month and one off payments of £118 for the router and switch over service. It's also unlimited calls 24/7, so seems perfect.

There are just a few considerations with the above option.

1... The router is only on loan. If she cancels the rolling contract the unit must be returned. Which means she cannot switch providers easily.

2... The provider uses the EE network. I bought a mobile from EE for an Xmas gift. This arrived in a plain plastic bag with no bubble wrap or addittional protection causing some scuffing to the box. Annoyed by this I did a Trust Pilot search and discovered a significant number of users disgruntled with both their EE broadband and mobile network services.

Just curious if anyone here in the UK has had a similar experience recently, or knows of a company offering similar services.
Google leads me to Voip services, but they all require a broadband connection, something my mother doesn't have.

I don't want something that requires workarounds, just a straight forward service that is easily implemented. It is not even critical she retains her old number.

Any advice greatly appreciated.

Thanks in advance.