I suggest you give yourself a sort of "holiday" first. It is very easy to get overcommitted as a sort of panic reaction to having no set things or times organised. Allow yourself to try out some pastimes you havent had the time for before, but keep it informal, rather than signing up for set times straight away.
If you take things steady for the next couple of months, in September there will be many courses and clubs and groups that you could explore. Firstly I suggest that you take yourself off to the library, where they will have quite a variety of notices about all sorts of things and they usually have all the up to date phone numbers and contacts for groups , whether the U3a, or the golf club or whatever. If you see anything that takes your fancy, you could look up more information on it. When you are considering things, remember to think of going to meetings in winter as well as summer and think if that would make any difference to you.
There are many lovely gardens open in the NGS , which are just lovely to visit in their own right and give you good ideas for your own garden - if you have one. Let your mind also get used to the change, and something you could do easily is to move your shopping and things like any business meetings you might need to weekdays and generally avoid the weekends. That can be something applied to trips away too. The pleasure of avoiding bank holiday weekends and so forth. Enjoy the summer being able to go out and about or just enjoy being at home and taking things easy.
There are very many different organisations who would be glad of a volunteer to help out. Again you could try some things out before committing yourself to a regular date, as you may find things different to how you had expected. Then when you find the things you enjoy doing , to be a reliable volunteer is very much appreciated.
Finally have you had something or somewhere you always fancied going to but never got there? If you are in reasonable health I always think it is a good plan to see if you could go, while you are able to. We never know what changes in our lives, and finally getting to that special place is very worth while even if it does not live up to your expectations. So my motto is do and go while you can. I think it is better to have done things and look back at new horizons tried than to stay at home , never get there and wish you had. Whether that turns out to be travelling far and wide or going to part of this country that you have never been to before.
I hope you enjoy trying out some ideas that you will see from posts on here and dont forget, you can try out lots at your own pace. You are not stuck with cramming everything into a few weeks. You might also keep a little notebook with you, so that at one end you jot down any ideas of things you would like to try or do. At the other end you could put down any jobs or things that need doing, getting paperwork up to date, checking address and phone numbers up to date on the endless pile of papers. If you drive is your photo up to date on your licence? Have you applied for your bus pass if you are entitled to one. This is not meant to be a list to make you feel you must do any specific thing, but the ideas are there as and when you want them.
In the meantime you can really enjoy right now, sitting in the cool inside or out ,in the middle of the day , with a cold drink and just think how glad you are not to be stuck in a stuffy office or boiling in a car on the motorway. You will soon find yourself wondering how you had time to go to work, as many people say