You must start a campaign on your Mother. It's Mother 'attack' time but subtlely and over a concerted period. Prove to her that a Corgi in the house will work out fine and it is really what she would enjoy if not love. Corgis are not dogs - they are something else.
I read six short stories based on my Pem, Taylor yesterday to a young audience at a large public library and Taylor was simply adored by the children and adults. A Corgi can have this kind of affect on a wide spectrum of ordinary people.
You sound as though you have what it takes to give a Corgi all the care and attention he/she needs. But you certainly need the co-operation of your mum. Corgis are an easy little creature to raise and provide for.