My parents live in Gorleston and I think it probably meets all your needs. It is a medium sized town, neither rural nor touristy and if you watch the film Yesterday a lot of it was shot in Gorleston.
You can walk from one end to the other in 30 mins. The High Street has a fairly large library, cinema, a wilko, a Morrisons, Iceland and Farm foods, a mixture of different pubs, restaurants and cafes as well as some more boutique shops. There is a night club, pub, small theatre and amusement arcade on the beach front but it isn't hectic or touristy like Yarmouth. If you prefer countryside you can walk (or get the bus) to Burgh Castle and do the Riverside walk next to Breydon Water.
There are several gyms in Gorleston and then a 25 m pool in nearby Bradwell and a brand new sports centre with pools and flumes being built in GY at the moment.
The James Paget hospital has a bus station and my parents have always had quick and brilliant care there and waiting times at A & E are normally under 2 hours (not at the moment due to Covid).
Buses run every 10 minutes towards Gt Yarmouth or every 30 mins to Lowestoft and Norwich, where you can get another bus to Norwich Airport. You can get National Express coaches to London or other coach holidays from the High Street too. Or get the train from Gt Yarmouth and connect to national services in Norwich.
Housing goes from under £100k for a small terrace house to more than £1,000,000 so plenty of choice.
Broadband and phone signal are great, the same cannot be said for more rural areas of Norfolk, my parents have friends who only get signal in one area of their house etc. Also when we get heavy snowfall it's not unusual for some of the more remote villages and smaller coastal areas to get cut off due to the snow.
I think I've addressed every possible point but any questions just ask. My parents moved from London 30 years ago and don't regret it.