I had a bilateral mastectomy with DIEP flap reconstruction 20 days ago that lasted 15 hours. My feet have been numb and tingling

The fact that there is some improvement means that recovery is likely. However, you should be a neurologist just be check in an make sure nothing else is happening to cause this. There are medications that can help alleviate your symptoms and help you sleep.

Thank you very much for your interesting enquiry.It does sound as if it may be a positional
issue.In the surgery you are lying flat
and unable to move and sometimes the nerves in the back of your legs are
pressed whilst you are asleep.
Generally this nerve pain does settle with time as the
nerve recovers.
If the pain really is unbearable I think it would be
worthwhile discussing with your surgeon and there are tests they can do to
assess the nerves.Generally however,
nerves will heal with time and hopefully your pain will settle.AR

I am sorry to hear about the symptoms you are going through.  You may want to ask your PS about referring you to a neurologist who can start you on medication that will alleviate your pain.  But these symptoms usually get better with time.