I am sure you are aware of this already: do get outside for your daily exercise (if able and not self isolating) as it is so beneficial for your health and well being, especially as our skin can begin to make Vitamin D once more as winter light turns to summer. If you are self isolating but able to use your garden, maybe as well as gardening and relaxing with a book when warm enough, you could do some exercise there.
The internet is full of exercise ideas, including Joe Wick's daily video. Tom Goom on the Running Physio website found some research indicating that training for fifteen minutes, three times a week is enough to build on your strength and endurance and he has a video with some circuit training ideas:
I would recommend daily yoga for its calming influence, plus some cardio exercises to get your heart rate up. Skipping is excellent for this as are star jumps, lunges and squats (check your knee doesn't go too far forward), marching on the spot or even practicing sitting down and standing up again without using your arms (keep them folded across your chest to make sure your legs are doing the work and that your neck and back keep relaxed; as you get stronger you can do this one legged). Calf raises can be easily fitted in throughout the day, for instance when brushing your teeth. I have been practicing my hopping technique, doing a few repetitions on each leg and aiming to develop a springy 'up' impulse. You can use your bottom stair or doorstep for step ups and you may also want to investigate using household items for a bit of upper body work out. Do exercise safely, though! If something doesn't feel right, stop and do something easier. If you are trying something new, just do a few to begin with and see how you feel a day or two later before increasing the exercise. Start easy and build up.
Yoga with Adriene is an excellent free source for yoga on Youtube https://www.youtube.com/user/yogawithadriene/videos and many yoga practitioners are now streaming their classes, for instance my friend and yoga practitioner Claire Latimir of Holistic Heaven is streaming classes on her Facebook page. The Reach in Sheffield is also doing online classes via Zoom so the teacher can keep an eye on the class:
The yoga sequence Sun Salutation is wonderful for extending, flexing, connecting with how your body is feeling and relaxing; you can find videos demonstrating it on many yoga websites and Youtube.
You can also find T'ai Chi classes online, from schools that are streaming classes to Lockdown Tai Chi on Facebook who are offering free Zoom classes.
I have been recommended Evolve Life Somatics who are running free classes from their Facebook group. I have not tried their classes yet but I am very impressed with Somatic movement and it is something I am considering training in as it ties in very well with my JEMS training that incorporates elements of somatic movement.