Stop midway London to Edinburg

Coming back from Edinburgh from London our first time, we stayed in historic York. Fantastic place, although not exactly small, and not on the ocean. A few years ago, we stayed in Newcastle upon Tyne. It’s a great, historic city, but it’s bigger than York, although much closer to the sea. There are beaches just east of Newcastle, with suburban settlements.

There’s regular train service to either, from London’s Kings Cross station.

You could stay in Tynemouth https://englandsnortheast.co.uk/tynemouth/

You could stay in Alnmouth https://englandsnortheast.co.uk/alnmouth-dunstanburgh/

You could stay in Bamburgh https://englandsnortheast.co.uk/bamburgh/

You could stay in Berwick https://englandsnortheast.co.uk/berwick/

Or further south, there is Scarborough

Scarborough is hard to describe as a small, quiet or historic beach town. One of the other Yorkshire seaside resorts like Bridlington or Filey would better suit that description- on the Scarborough to Hull line, with direct trains on Hull trains from London Kings Cross to Hull.

If you are willing to forego the beach then Beverley would be a pretty good fit in that part of Yorkshire. The Hull trains service, above, starts/ends there.

There are also direct buses from York Railway Station to Beverley.

Thanks for all the answers. We decided on York as it will be a bit easier using the train. My husband does not like switching so I know going to one of the smaller seaside towns will entail that. . I figure we leave from London, go to York spend 3 nights. Then to Edinburgh for 5 nights then back to London. I assume the best train will be a the Liner back to London from Edinburgh. What is the best way to do the London to York and then York to Edinburgh.?
Any suggestions will be most helpful. I rather use a train and no buses. Shall I buy separate tickets for the train from London to York and then York to Edinburgh?