Here are 3 excercises that will boost your strength and cardio which you can do at home.
For strength, there is one arm push up and one legged squats.
Why these exercises are good is that using body weight and leverage is possible to put stresses on the body that would correspond to a couple of hundred pounds in the gym.
Here is how they are done :
One Arm Push up
One Legged Squats
For cardio excercise, you can do burpees. It can be done anywhere, even at home. If you can do it regularly, you do not need to go running to get your dose of cardio.
The key thing to note is to always do the exercise within your limits. If you are just comfortable doing 10, do 10 reps. Just make sure you do them regularly, like 5 days a week. If you push yourself too hard, you make take longer to recover and your consistency will drop. When you are not exercising consistently your mind still start to make excuses to not exercise. Which will defeat the purpose of it all.
Best is to know your limits and work around it, and make sure you do it consistently for the best results. Fitness is something you have to keep working at it, it is not like investing where you can put in a lump sum and reap the dividends forever. Create a schedule for exercising that you can stick to.