We did our first UK holiday this year as Borneo cancelled and had a lovely time.
We stayed at Watermouth Castle in North Devon (currently closed to public but 7 apartments open though 7 day bookings only) which overlooks harbour / coast. It was lovely - has a swimming pool and each apartment gets allocated 2 (or occassionally 1) hour per day for sole use so did that 3 days. Also have crazy snooker and golf and 50 acre beautiful gardens just open to apartments.
We did a boat trip to swim with seals and then go to Lundy Island where there were highland cattle and lots of other wild animals. If you are lucky you can see dolphins on way over. That was quite magical - the walking on Lundy was a challenge for me but you can get trips just swim with seals or even private charter and design own trip. I struggle with walking but Lundy was worth it, beautiful coastal scenery and wildlife and just the one old pub which we went to. You can ask for a car to take you to top if that helps or from October (?) onwards arrive by helicopter.
Then did trip along the Devon coast from Ilfracombe which was lovely 2.5 hours at sunset time with most beautiful skies and scenery, seeing seals, sometimes dolphins as well.
Then went gorging in river but this is not for those with walking or balance issues!! Great if you don't though and kids loved it, I had to stop after an hour but still great to try.
We drove around the coast and onto Dartmoor seeing extra fluffy sheep, wild ponies etc and beautiful scenery and going to a cottage there with alpacas and a hot tub with a cream tea waiting. Then the boys went on a walk across Dartmoor with llamas - I'm not capable but there was an option just to visit the farm and meet aplacas / llamas. Another option is horseriding across Dartmoor.
We had good weather 7/9, not sure what whether will be in September as not been then but its very south. The indoor pool we had was very useful for raining days, there were 2. Lots of lovely meals, Thai, Chinese, pizza, fish and chips by the sea.
If you can't walk round coast there are coastal roads you can drive on or boats, same with Dartmoor you can drive some of it or horseride. I think you can drive to the places seals are at. Steam trains in local area and a cliff railway in Lynton. We would all go back.