I've been the same, as I have asthma, and have not wanted to take nay risks withe the virus, so have stayed indoors for a year now. I think I would have found a way to do more if I'd realised how long this was going to go on, but hindsight is a wonderful thing.
I recently bought a 'cycle' thing that is intended to go under the desk of office workers, and plan to build up to a couple of miles on that. I'll have to take it slowly, though, as I'm so out of condition. I know it's not the same as getting fresh air, but at this stage I feel as though I should wait until I get my vaccination - after all this time I don't see the point in taking risks now.
When I've been vaccinated I hope I'll feel more confident about going out, even if it's to places where there are very few people.