What would be a good place to base in Cornwall if I don't have a car and can't do much hiking
Because of the geography, you can't move around Cornwall very rapidly by public transportation. I suspect that even those with cars often end up splitting their time between two bases unless they are satisfied to focus on just one part of the region.
Those who know the area well will be able to help you more if they know what places you hope to visit in Cornwall.
If I had to name one area of England that I wouldn’t go without a car, it would be Cornwall, as public transport isn’t great there, as you will see if you look at a rail map.
What do you want to do and see there? When would you be travelling?
I much prefer the southern Cornish coast and would stay in places such as Mevagissey, Fowey, Feock and St Mawes. Personally, following the Doc Martin series, I would avoid Port Isaac like the plague, as it’s overrun with series groupies. Truro would be a good base.
We had a week long trip to Cornwall and Devon for this July, but had to cancel because of the virus.
We planned two nights in Exeter, then renting a car and moving on to Truro for four nights.
I found tours from London of Cornwall, but wasn't pleased with them. Also, the day tours that I found were very expensive.
Basically echoing the advice of the above comments, but I went to St. Michael's Mount (right by Marazion) by bus from Truro and enjoyed it very much. I'd read about the Mount in National Geographic when I was in grade school and always wanted to go there. I wasn't disappointed.
Truro is the only city in Cornwall and I'd say it's the closest thing to a major transportation hub. Your public transportation options from Truro will be better than from elsewhere. But, again, it depends on what you personally want to see and experience.
Thanks to the 4 who answered. I have been to Mousehole, St. Ives, Penzance, and St. Michel's Mount in the past so they are not high on my list. I like what I have seen in videos of the south coast but because we are in our 70's I am afraid trying to drive might be frightening and some rental car companies cut off the age limit for rentals at 70. I was hoping to use public transportation as I did back in 1990. As this would be at the end of our two week holiday in England next spring I was hoping to relax and breath in the fresh sea air and do some mild hiking ( no more than 3miles). I really like Megavissy from what I have seen and was hoping to base there. I know that there is transport from St. Austell which is nearby. One day I would like to go back to St. Ives to see the art galleries there. My husband loves sailing and history. Any other ideas welcomed.
The additional information helps a lot. I actually stayed in Mevagissey in 2017 in order to see the Lost Gardens of Heligan and The Eden Project. Both can be done by public transportation, though possibly not on the same day. In any case they're both large, so I wouldn't want to rush them. I didn't have time to go to Falmouth, but it sounds interesting, too, and Truro is worth a visit as well.
Mevagissey is small but has a traffic problem--not a problem for you if you don't intend to drive. Get clear directions about where to get the outbound bus and show up early. I ended up having to walk to one of the gardens; I think it was Heligan. It wasn't terribly far but it wasn't exactly a groomed trail and it had been raining...
One thing about Cornwall that you may already know if your previous trip wasn't too long ago: If you hope to eat dinner while seated at a table, you need to make a reservation. The infrastructure just doesn't seem to have kept up with the demand from fans of Poldark and Doc Martin. I also found there was no ATM in Mevagissey. That situation may have been remedied by now, but I recommend not showing up with just a few pounds in your wallet, as I did.
There is now an ATM at the Post Office in Mevagissey. The general point stands that you can't rely on one being in every Cornish town/village though.