We’re roughly same age range with same achey joints.
We holiday in U.K. quite often and do quite different things in different places. We also like holidays abroad and sunshine but not generally just sunlounger, all inclusive, places. It might be fun to try new things.
Try thinking about
Boating holiday - a barge or canal boat somewhere nice is gentle fun, with nice pub meals, pleasant flat walks etc.
Lake District near Keswick- the launch, nice meals, Honister slate mine, a nice Spa hotel at Lodore, gentle but beautiful walking around the lake, swimming in the lake if you’re feeling brave.
Snape Maltings have a lovely old barge to hire or a cheaper AirbnB. Nice pubs, the Suffolk Coast, pottering around Aldeburgh, Southwold. Orford Castle, kayaking on the river or boat trips, a few day trips out.
A city break in York or overnight sleeper train and Edinburgh. Or a two city break or motor tour staying at gastro pubs and seeing hidden England. Maybe up one coast or going coast to coast.
Dartmouth or nearby is lovely regardless of weather. Boat trip on Dart or out to sea. Fabulous restaurants, nice beaches if you get some good weather. Dartmouth Castle, lots of NT places. The train/boat/ bus circular. Dartmoor. Darlington glass. A swim in the Dart, if you want an exhilarating feeling.
Isle of Wight is a bit mixed. Some of the lovelies beaches and countryside in the South. Microclimate on south of island so tends to get better weather. Good NT and EH places to visit. Some quirky places like the garlic farm. Huge range of accommodation to suit all pockets and tastes. Very good swimming. Very foodie, with excellent local produce. Good for dogs. Ferry adds to holiday feeling.