Just because I've been there and done it doesn't mean that you can. You know your limitations, I don't, so if you go there it is at your own risk. By mentioning the place I'm not suggesting that you go there.
Trebah and Glendurgan, Mawnan Smith, Falmouth, Cornwall, TR11 5JZ
Trebah Garden, Cornwall is one of those places that, if I was local, I'd want to revisit time and time again. The sub-tropical garden is wonderful and access by their hired off-road mobility scooter, a Tramper provided by Countryside Mobility, even took me onto the beach, with care to avoid soft sand. There are more than 4 miles of footpaths, so take your time.
The restaurant is also good, the shop is interesting - especially for dog toys, and the toilets include disabled ones. self-propelled wheelchair access would be tough going, so hire the Tramper instead (book ahead).
If practicable do approach Trebah from the east, we ddin't, the Cornish road from the west is very narrow even by Cornish standards.
Glendurgan, next door, is owned by the National Trust and whilst good has not had the investment that Trebah has. There Countryside Mobility have also provided a Tramper which can be taken to the beach at Durgan, a tiny hamlet on the helford estuary, home to just 10 residents, a small cafe, and holiday cottages with fabulous views, owned by the Natoinal Trust. Glendurgan is well known for its giant rhubarb, bamboo, and banana plants.