Physical activity can easily be included in your daily routines free of charge. Take a look at your habits. Maybe you spend a lot of time on your sofa. Even though it is very probably very comfortable you might need to ease up your relationship. Because each step you take, boosts your health. For example:
How about running a few errands on foot instead of taking the bus or car. It is easiest to start small: get off the bus a bus stop earlier than your actual destination. Or park your car around the corner instead of directly by your doorstep.
Try setting targets for yourself and then reward yourself. For example you could plan a trip to the local farmers market together with a friend, buy some groceries and then cook a delicious meal together. Or maybe you would rather arrange to check out a new cafe (and of course go to the meeting point on foot or maybe take a stroll afterwards).
If you are not into shopping and cafes, how about a new project such as decluttering the cellar or the garage and organizing a car boot sale or fleamarket together with your neighbours. Or re-decorate a room you have been wanting to change for ages.
...that is the question. You certainly need to adapt the extent of your exercise, if you have issues with e.g. your knees only put weight on them as far as you feel comfortable.
Swimming is a good choice if you have joint pain or are overweight, as you can gently train your muscles which will in turn take the pressure off your joints in future.
Alternatively, cycling is also a good option to strengthen the muscles in your legs.
But you do not necessarily need to leave the house to be active: cleaning the windows, changing the sheets or tidying up are all activities during which you can work up a sweat - and that is a good thing!
A quick example...
Description
The next time your visit to the doctors office takes a little longer - why not use the time?
Sit up straight in your chair an plant both feet firmly on the ground. Now try pulling up your feet one at a time while keeping the heel attached to the floor. Move your feet alternatingly: left-right-left-right.
As a second step "open and close" you feet by moving your toes to the side, while leaving your heels centred and on the floor.
And you can also lift your whole foot of the ground. Try doing this exercise slowly and keeping you foot in mid-air for a brief moment.
Now you can do the routine the other way around. Keep your toes on the floor while lifting your feet.
After that you can turn to your fingers. Try touching each finger of one hand to the thumb of that hand. Try the exercise for each hand separately and then both hands together.
This exercise is good for your circulation while also training your cognitive skills.