I have challenge for you. How about if tonight you put the pulse oximeter in the medicine cabinet when you brush your teeth. Tomorrow just use it before you brush and put it away. Try to keep going all day by being active at least 20 minutes at a time - longer if you feel okay.

You also said you have no one to put a chair outside for you. Can you ask a neighbor or manager or maintenance person for help?
I know you can do this, even if it is hard!
Sue