Enigma, I just want to add a bit from a mother's point of view and also from a daughter's point of view as I am both having brought up two children the oldest being 37.
I know this is a metaphysical website and not an agony aunt column but as I have no experience in the advice BW gave you( which must be worth trying) then I'm trying to see it from both sides.
Firstly why should any of us have any negative views on your living situation? You may not see it but you are so lucky to have what you have. ( okay yes I'm saying this as a mother's view) Help on hand. Company on hand. If your ill your parents to look after you living above. If your child is ill you have help. Many single parents do not live like this and do not have the support of their parents as you do. Also your landlady will probably never throw you out for non payment of rent.
So to end this little ' How Lucky Am I ' lecture it may be that your mother is loving having you around with her grandchild on tap so to speak. She still wants to mother you , to show an interest in your interests. Could it be that she is concerned about your future prospects and how you will support yourself and child in the future?

Now on to you.
Obviously what you lack is privacy.
I don't know how the structure is when it comes to basements . Do you have your own door.?
*** Could you put a bolt on and use this at night and during meditation? ( discreetly explaining the reason why)
***Could you switch off your mobile and use other device to listen to music?
***could you talk to others who live upstairs and get them on your side and ask them to keep your mum away at those times?

With me I used to be convinced my mother had a video camera secretly hidden and focusing on my front door. Every day rushing in from work dying for the loo and the phone would go. My mother! No news, just hello. I used to be wriggling trying to say goodbye.
Every Sunday her car would pull up at 12 after she had been to a car boot sale. I would run to get a duster and polish in my hand and continue to polish as she sat there trying to talk to me. I couldn't get the message through strongly enough. When she left I would feel more guilt than relief. How I wish the phone would ring again.
My son on a visit from uni has been known to send a text message from his phone whilst upstairs in bed to my phone downstairs in the kitchen asking me if I would like to start his breakfast now , he would be down in a minute and a full breakfast would be nice.
I wouldn't change anything.
All I'm saying is that it sounds it's very frustrating for you just now but one day you will look back and laugh.
I would give BW advice a try.